[rust] init multipass cargo workspace & oxidize petname

[levkropp]

This pull request introduces Rust to Multipass by migrating the petname (name generation e.g. hearty-kangaroo) functionality from C++ to Rust and integrates it into the build and runtime environments. This transition involves replacing the old C++ name generator with a new Rust implementation, updating the build system to compile and link the Rust static library, and adapting relevant CI and packaging scripts to support Rust. The changes also update C++ code to use the Rust FFI for name generation and remove legacy C++ petname code.

Petname/name generation migration to Rust:

• Added new Rust crate (tentatively named rustipass) and implemented petname in rust as a module, exposing FFI functions for name generation and tests.
• Updated C++ code (src/client/gui/ffi/dart_ffi.cpp, src/daemon/daemon.cpp) to use Rust FFI for petname generation instead of the old C++ NameGenerator.
• Removed legacy C++ petname and name generator code (include/multipass/name_generator.h, src/petname/make_name_generator.cpp).

Build system and CI integration:

• Updated CMake configuration to build the Rust static library and link it as an interface library for petname, removing previous code-generation steps. (src/petname/CMakeLists.txt)
• Added Rust-related files to CI triggers and installed Rust toolchain in CI workflows for Windows/macOS (.github/workflows/dynamic-ci.yml, .github/workflows/windows-macos.yml).

Packaging and environment updates:

• Added Rust as a build dependency and ensured the Rust toolchain is initialized during Snap builds and CI (BUILD.*.md, snap/snapcraft.yaml)

Daemon configuration cleanup:

• Removed all references to the old C++ NameGenerator from daemon configuration code (src/daemon/daemon_config.cpp, src/daemon/daemon_config.h).

MULTI-2218

[codecov]

Codecov Report

❌ Patch coverage is 93.43066% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.30%. Comparing base (68ede90) to head (3c2af6c).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rustipass/rust_petname_generator.cpp	42.85%	8 Missing ⚠️
src/daemon/daemon.cpp	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4299      +/-   ##
==========================================
+ Coverage   89.28%   89.30%   +0.02%     
==========================================
  Files         260      261       +1     
  Lines       17532    17636     +104     
==========================================
+ Hits        15653    15750      +97     
- Misses       1879     1886       +7     

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