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-core/Cargo.toml

@@ -0,0 +1,12 @@
+
+[package]
+name = "api-core"
+edition = "2021"
+version = "0.1.0"
+authors = ["Sergey <me@sergeysav.com>"]
+
+[dependencies]
+chrono = { workspace = true, features = ["serde"] }
+derive_more = { workspace = true, features = ["display", "from", "try_into"] }
+serde = { workspace = true, features = ["derive"] }
+thiserror = { workspace = true }