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>

Cargo.toml

@@ -1,6 +1,33 @@
 [workspace]
-members = ["server", "examples/simple_producer", "examples/simple_command"]
+members = ["api", "api-core", "api-proc-macro", "server", "examples/simple_producer", "examples/simple_command"]
 resolver = "2"
 
+[workspace.dependencies]
+actix-web = "4.12.1"
+actix-ws = "0.3.0"
+anyhow = "1.0.100"
+chrono = { version = "0.4.42" }
+derive_more = { version = "2.1.1" }
+env_logger = "0.11.8"
+fern = "0.7.1"
+futures-util = "0.3.31"
+log = "0.4.29"
+num-traits = "0.2.19"
+papaya = "0.2.3"
+proc-macro-error = "1.0.4"
+quote = "1.0.42"
+serde = { version = "1.0.228" }
+serde_json = "1.0.148"
+sqlx = "0.8.6"
+syn = "2.0.112"
+thiserror = "2.0.17"
+tokio = { version = "1.48.0" }
+tokio-test = "0.4.4"
+tokio-stream = "0.1.17"
+tokio-tungstenite = { version = "0.28.0" }
+tokio-util = "0.7.17"
+trybuild = "1.0.114"
+uuid = { version = "1.19.0", features = ["v4"] }
+
 [profile.dev.package.sqlx-macros]
 opt-level = 3