feat(nix): allow treefmt.nix based setups

[isbecker]

• enables better behavior for files with no extensions
• enables formatting unsaved files, if they have a selected filetype

[Copilot]

Pull request overview

This pull request adds support for treefmt.nix-based setups and improves handling of files with no extensions. The main changes include enhanced stdin specifier generation, improved command resolution with executable validation, and migration from .treefmt.toml configuration to flake-based treefmt-nix setup.

Key Changes

• Command resolution improvements: Added validation to check if treefmt commands are executable before using them, with fallback logic to check PATH and bundled binaries
• Enhanced stdin handling: New logic to infer appropriate file extensions or names for stdin formatting based on VS Code's language ID mappings, improving support for files without extensions
• treefmt-nix integration: Migrated from standalone .treefmt.toml to flake-based treefmt-nix configuration with declarative formatter setup

Reviewed changes

Copilot reviewed 11 out of 13 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/treefmtUtils.ts	Added helper functions for tilde expansion, path detection, stdin specifier generation, and command validation
package.json	Version bump to 2.4.0, added .treefmt.toml activation event, changed debug default to true
package-lock.json	Updated dependencies to match package.json changes
flake.nix	Integrated treefmt-nix module with declarative formatter configuration
flake.lock	Updated lock file with treefmt-nix and dependency version updates
biome.json	Updated schema version and reorganized import settings
esbuild.js	Code formatting changes (quotes, spacing)
README.md	Formatting improvements for badge layout
LICENSE.md	Added markdown code block formatting to license text
.vscode-test.mjs/.js	Quote style changes
.treefmt.toml	Removed standalone configuration file
.github/workflows/format.yaml	Updated to use Nix devShell and system treefmt

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