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>

examples/simple_command/Cargo.toml

@@ -4,11 +4,9 @@ name = "simple_command"
 edition = "2021"
 
 [dependencies]
-server = { path = "../../server" }
-tonic = "0.12.3"
-tokio = { version = "1.43.0", features = ["rt-multi-thread", "signal"] }
-chrono = "0.4.39"
-tokio-util = "0.7.13"
-num-traits = "0.2.19"
-log = "0.4.29"
-anyhow = "1.0.100"
+anyhow = { workspace = true }
+api = { path = "../../api" }
+env_logger = { workspace = true }
+log = { workspace = true }
+tokio = { workspace = true, features = ["rt-multi-thread", "signal"] }
+tokio-util = { workspace = true }