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/src/client/error.rs

@@ -0,0 +1,37 @@
+use api_core::data_type::DataType;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum ConnectError {
+    #[error(transparent)]
+    TungsteniteError(#[from] tokio_tungstenite::tungstenite::Error),
+    #[error(transparent)]
+    IoError(#[from] std::io::Error),
+}
+
+#[derive(Error, Debug)]
+pub enum MessageError {
+    #[error(transparent)]
+    TokioSendError(#[from] tokio::sync::mpsc::error::SendError<()>),
+    #[error(transparent)]
+    TokioTrySendError(#[from] tokio::sync::mpsc::error::TrySendError<()>),
+    #[error(transparent)]
+    TokioLockError(#[from] tokio::sync::TryLockError),
+    #[error("Incorrect Data Type. {expected} expected. {actual} actual.")]
+    IncorrectDataType {
+        expected: DataType,
+        actual: DataType,
+    },
+}
+
+#[derive(Error, Debug)]
+pub enum RequestError<E> {
+    #[error(transparent)]
+    TokioSendError(#[from] tokio::sync::mpsc::error::SendError<()>),
+    #[error(transparent)]
+    TokioLockError(#[from] tokio::sync::TryLockError),
+    #[error(transparent)]
+    RecvError(#[from] tokio::sync::oneshot::error::RecvError),
+    #[error(transparent)]
+    Inner(E),
+}