Replace gRPC Backend (#10)

**Rationale:**

Having two separate servers and communication methods resulted in additional maintenance & the need to convert often between backend & frontend data types.
By moving the backend communication off of gRPC and to just use websockets it both gives more control & allows for simplification of the implementation.

#8

**Changes:**

- Replaces gRPC backend.
  - New implementation automatically handles reconnect logic
- Implements an api layer
- Migrates examples to the api layer
- Implements a proc macro to make command handling easier
- Implements unit tests for the api layer (90+% coverage)
- Implements integration tests for the proc macro (90+% coverage)

Reviewed-on: #10
Co-authored-by: Sergey Savelyev <sergeysav.nn@gmail.com>
Co-committed-by: Sergey Savelyev <sergeysav.nn@gmail.com>

api-proc-macro/tests/test_derive_macro_into_command_definition.rs

@@ -0,0 +1,170 @@
+use api_core::command::{
+    Command, CommandHeader, CommandParameterDefinition, IntoCommandDefinition,
+};
+use api_core::data_type::DataType;
+use api_core::data_value::DataValue;
+use api_proc_macro::IntoCommandDefinition;
+use std::collections::HashMap;
+
+#[test]
+fn test_enum_fails() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/into_command_definition/enum_fails.rs");
+}
+
+#[test]
+fn test_union_fails() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/into_command_definition/union_fails.rs");
+}
+
+#[test]
+fn test_unnamed_struct_fails() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/into_command_definition/unnamed_struct_fails.rs");
+}
+
+#[test]
+fn test_basic_command() {
+    #[derive(IntoCommandDefinition)]
+    struct TestStruct {
+        #[allow(unused)]
+        a: f32,
+        #[allow(unused)]
+        b: f64,
+        #[allow(unused)]
+        c: bool,
+    }
+
+    let command_definition = TestStruct::create("Test".to_string());
+
+    assert_eq!(command_definition.name, "Test");
+    assert_eq!(command_definition.parameters.capacity(), 3);
+    assert_eq!(
+        command_definition.parameters[0],
+        CommandParameterDefinition {
+            name: "a".to_string(),
+            data_type: DataType::Float32,
+        }
+    );
+    assert_eq!(
+        command_definition.parameters[1],
+        CommandParameterDefinition {
+            name: "b".to_string(),
+            data_type: DataType::Float64,
+        }
+    );
+    assert_eq!(
+        command_definition.parameters[2],
+        CommandParameterDefinition {
+            name: "c".to_string(),
+            data_type: DataType::Boolean,
+        }
+    );
+
+    let mut parameters = HashMap::new();
+    parameters.insert("a".to_string(), DataValue::Float32(1.0));
+    parameters.insert("b".to_string(), DataValue::Float64(2.0));
+    parameters.insert("c".to_string(), DataValue::Boolean(true));
+    let result = TestStruct::parse(Command {
+        header: CommandHeader {
+            timestamp: Default::default(),
+        },
+        parameters,
+    })
+    .unwrap();
+    assert_eq!(result.a, 1.0f32);
+    assert_eq!(result.b, 2.0f64);
+    assert_eq!(result.c, true);
+}
+
+#[test]
+fn test_generic_command() {
+    #[derive(IntoCommandDefinition)]
+    struct TestStruct<T> {
+        #[allow(unused)]
+        a: T,
+    }
+
+    let command_definition = TestStruct::<f32>::create("Test".to_string());
+    assert_eq!(command_definition.name, "Test");
+    assert_eq!(command_definition.parameters.capacity(), 1);
+    assert_eq!(
+        command_definition.parameters[0],
+        CommandParameterDefinition {
+            name: "a".to_string(),
+            data_type: DataType::Float32,
+        }
+    );
+    let mut parameters = HashMap::new();
+    parameters.insert("a".to_string(), DataValue::Float32(1.0));
+    let result = TestStruct::<f32>::parse(Command {
+        header: CommandHeader {
+            timestamp: Default::default(),
+        },
+        parameters,
+    })
+    .unwrap();
+    assert_eq!(result.a, 1.0f32);
+
+    let command_definition = TestStruct::<f64>::create("Test2".to_string());
+    assert_eq!(command_definition.name, "Test2");
+    assert_eq!(command_definition.parameters.capacity(), 1);
+    assert_eq!(
+        command_definition.parameters[0],
+        CommandParameterDefinition {
+            name: "a".to_string(),
+            data_type: DataType::Float64,
+        }
+    );
+    let mut parameters = HashMap::new();
+    parameters.insert("a".to_string(), DataValue::Float64(2.0));
+    let result = TestStruct::<f64>::parse(Command {
+        header: CommandHeader {
+            timestamp: Default::default(),
+        },
+        parameters,
+    })
+    .unwrap();
+    assert_eq!(result.a, 2.0f64);
+
+    let command_definition = TestStruct::<bool>::create("Test3".to_string());
+    assert_eq!(command_definition.name, "Test3");
+    assert_eq!(command_definition.parameters.capacity(), 1);
+    assert_eq!(
+        command_definition.parameters[0],
+        CommandParameterDefinition {
+            name: "a".to_string(),
+            data_type: DataType::Boolean,
+        }
+    );
+    let mut parameters = HashMap::new();
+    parameters.insert("a".to_string(), DataValue::Boolean(true));
+    let result = TestStruct::<bool>::parse(Command {
+        header: CommandHeader {
+            timestamp: Default::default(),
+        },
+        parameters,
+    })
+    .unwrap();
+    assert_eq!(result.a, true);
+}
+
+#[test]
+fn test_unit_command() {
+    #[derive(IntoCommandDefinition)]
+    struct TestStruct;
+
+    let command_definition = TestStruct::create("Test".to_string());
+
+    assert_eq!(command_definition.name, "Test");
+    assert_eq!(command_definition.parameters.capacity(), 0);
+
+    TestStruct::parse(Command {
+        header: CommandHeader {
+            timestamp: Default::default(),
+        },
+        parameters: HashMap::new(),
+    })
+    .unwrap();
+}