refactor: consolidate TOML parsers to smol-toml

Replace fast-toml (TOML 0.5, unmaintained) with smol-toml (TOML 1.0,
actively maintained) in the Gradle provider, unifying the codebase on
a single TOML library.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Strum355