feat: Add TOML language support via Taplo

[w0wl0lxd]

Summary

• Add TOML language server using Taplo with automatic binary download for .toml file validation, formatting, and schema support
• Implement security hardening: SHA256 checksum verification, zip slip protection, download timeout
• Enable serena project index to work on projects with TOML in their language configuration

Fixes

Fixes #796

Details

TOML Language Support

• New TaploServer class in src/solidlsp/language_servers/taplo_server.py
• Automatic Taplo binary download for Windows, macOS, and Linux (x86_64, x86, aarch64, armv7)
• LSP integration for document symbols, hover, completion, and formatting
• TOML-specific directory ignore patterns (target, .cargo, node_modules)

Security Features

• SHA256 checksum verification: Validates downloaded binaries against hardcoded hashes from official Taplo 0.10.0 releases
• Zip slip protection: Validates archive paths to prevent directory traversal attacks
• Download timeout: 120-second timeout prevents indefinite hangs on network issues

Issue Resolution

When project.yml contains languages: ["toml"] but TOML isn't in the Language enum, ProjectConfig.load() raises ValueError: 'toml' is not a valid Language. This commonly occurs in Rust projects where users want to index Cargo.toml alongside .rs files. Adding TOML to the Language enum resolves this.

Test Plan

• [ ] Run uv run poe test -m toml to verify TOML language server tests pass
• [ ] Test on a Rust project with languages: ["toml"] in project.yml
• [ ] Verify Taplo auto-downloads correctly on first use
• [ ] Confirm SHA256 verification works (modify hash to test rejection)