fix(core): Comprehensive fixes and performance optimizations

[ehfd]

Complementary to selkies-project/selkies#254. Backward-incompatible components.

[PMohanJ]

I've reviewed the core module. The build is successful; deployed and verified in selkies container - no regression bugs.

[Copilot]

Pull request overview

This PR migrates pcmflux from a C++ shared library + Python ctypes wrapper to a single native Rust (PyO3) extension module, and updates the example server/client to match the new zero-copy AudioFrame callback API and wire framing.

Changes:

• Replaces the C++/ctypes implementation with a Rust pcmflux PyO3 extension (PulseAudio capture, Opus encoding, silence gate, WS framing + RED support, lifecycle safety).
• Updates Python packaging/build configuration to build the Rust extension via setuptools-rust and adjusts sdist contents.
• Updates the demo server/client to consume the new callback signature, avoid extra copies, and improve backpressure/monitoring.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
setup.py	Switches packaging to build a Rust PyO3 extension; sets default RUSTFLAGS for x86_64.
README.md	Expands usage/API documentation for the new callback + framing, but contains outdated C++/ctypes references.
pyproject.toml	Adds setuptools-rust and updates cibuildwheel configuration/provisioning for Rust builds.
pcmflux/src/lib.rs	New Rust implementation of capture/encode pipeline + PyO3 API types and tests.
pcmflux/Cargo.toml	New Rust crate manifest for the PyO3 extension and native deps.
pcmflux/Cargo.lock	Locks Rust dependency graph for reproducible builds.
pcmflux/audio_capture_module.cpp	Removes the prior C++ PulseAudio/Opus implementation.
pcmflux/init.py	Removes the prior Python ctypes wrapper API.
MANIFEST.in	Updates sdist include/exclude rules for Rust sources and build artifacts.
example/index.html	Updates client to strip the new 2-byte header, use monotonic timestamps, and add worklet/backpressure reporting.
example/audio_to_browser.py	Updates server to use the new Python API/callback and improves queue bounding, fan-out, and HTTP path hardening.

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