Use in-process GIO for Linux proxy settings

[Christof Marti (chrmarti)]

Summary

Replace the Linux dconf / gsettings child processes with runtime-loaded, in-process GIO configuration reads and change notifications.

• load GLib, GObject, and GIO dynamically so headless and musl environments do not gain hard system-library dependencies
• read org.gnome.system.proxy through typed GSettings APIs
• dispatch root and child-schema changes on a private GLib main-context thread
• stop and join the watcher cleanly without child-process or inherited-file-descriptor handling
• raise the repository MSRV to Rust 1.94 and enforce it in CI
• align the Rust crates, npm facade, and all platform packages on version 0.5.0

Validation

• full Rust test suite with the native PAC backend
• isolated dbus-run-session tests for typed reads and root/child notifications
• Rust 1.94 checks for all root features/targets and the Node addon
• Linux Node addon build and smoke test
• verified no hard ELF dependency on GIO, GLib, or GObject
• formatting, Clippy, lockfile, package manifest, and third-party notice checks

[Copilot]

Pull request overview

Replaces Linux proxy subprocesses with runtime-loaded GIO while avoiding hard GLib dependencies.

Changes:

• Adds typed GSettings reads and in-process change watching.
• Raises MSRV to Rust 1.94 and adds CI enforcement.
• Prepares npm packages for version 0.5.0.

Show a summary per file

File	Description
src/platform/gio.rs	Implements dynamic GIO access and watching.
src/platform/linux.rs	Integrates GIO proxy configuration.
src/platform/mod.rs	Updates watcher documentation.
README.md	Documents Linux GIO behavior and MSRV.
CHANGELOG.md	Records the 0.5.0 changes.
Cargo.toml	Raises MSRV and adds libloading.
Cargo.lock	Locks libloading.
pac-wasm-guest/Cargo.toml	Raises guest MSRV.
npm/native/Cargo.toml	Raises addon MSRV.
npm/native/Cargo.lock	Updates addon dependencies.
package.json	Bumps facade and platform dependencies.
npm/platforms/darwin-arm64/package.json	Bumps package version.
npm/platforms/darwin-x64/package.json	Bumps package version.
npm/platforms/linux-arm-gnueabihf/package.json	Bumps package version.
npm/platforms/linux-arm64-gnu/package.json	Bumps package version.
npm/platforms/linux-arm64-musl/package.json	Bumps package version.
npm/platforms/linux-x64-gnu/package.json	Bumps package version.
npm/platforms/linux-x64-musl/package.json	Bumps package version.
npm/platforms/win32-arm64-msvc/package.json	Bumps package version.
npm/platforms/win32-x64-msvc/package.json	Bumps package version.
ThirdPartyNotices.txt	Adds the libloading license.
.github/workflows/ci.yml	Adds Rust 1.94 MSRV checks.

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• Files reviewed: 20/22 changed files
• Comments generated: 3
• Review effort level: Balanced