fix(rt): prevent GIL from stalling background Rust future tasks

[0x676e67]

ref: PyO3/pyo3-async-runtimes#58

[Copilot]

Pull Request Overview

This PR implements a custom Rust async runtime to prevent GIL (Global Interpreter Lock) from stalling background Rust future tasks. This addresses PyO3/pyo3-async-runtimes issue #58 by replacing the external pyo3-async-runtimes dependency with an internal runtime implementation.

Key changes:

• Added custom async runtime module (rt/) with task locals and thread-safe execution
• Replaced all pyo3_async_runtimes::tokio calls with the new Runtime implementation
• Added new exception type RustPanic for better error handling

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/rt/mod.rs	Core runtime implementation with global Tokio runtime and task-local context management
src/rt/util.rs	Utility functions for setting Python future results and thread-safe callbacks
src/rt/task.rs	Task management with Python asyncio integration and context variable handling
src/rt/sync.rs	Synchronization primitives including cancellable futures and channel senders
src/lib.rs	Updated all HTTP method functions to use new Runtime instead of pyo3-async-runtimes
src/client/mod.rs	Updated client request methods to use new Runtime
src/client/resp/http.rs	Updated response processing to use new Runtime
src/client/resp/ws/mod.rs	Updated WebSocket operations to use new Runtime
src/client/resp/stream.rs	Updated streaming operations to use new Runtime
src/client/nogil.rs	Updated GIL-release functionality to use new Runtime
src/client/body/mod.rs	Updated body processing to use new Runtime
src/client/body/multipart.rs	Updated multipart form handling to use new Runtime
src/error.rs	Added new RustPanic exception type
Cargo.toml	Removed pyo3-async-runtimes dependency and added required tokio features

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