When stdin is a pipe (not a TTY), spawn a background thread that
monitors for EOF. This allows a parent process (such as the test
harness) to signal a graceful shutdown by closing stdin, without
relying on signals or lock file removal.

Add mtime and content-hash based deduplication to filter out phantom
and duplicate file system events. Normalize event kinds from atomic
writes (temp file + rename) so they are treated as content modifications
rather than create/remove cycles that trigger unnecessary full rebuilds.

This fixes issues on macOS (Create events from atomic writes), Linux
(duplicate inotify IN_MODIFY events), and Windows (Remove+Rename
sequences from atomic writes).

On Windows, bsc writes CRLF to stdout in text mode. When the original
source file uses LF line endings, the formatted output would introduce
unwanted CRLF conversions. Detect the original file's line ending style
and normalize the formatted output to match.

Add 7 new fixture packages to cover more configuration dimensions:
- commonjs: CommonJS module output with .bs.js suffix
- namespaced: namespace package with TestNS
- noop-ppx: lightweight cross-platform no-op PPX for testing
- with-deps: package depending on rescript-bun for clean tests
- with-dev-deps: multi-source dirs with dev dependencies
- with-jsx: JSX v4 with @rescript/react
- with-ppx: PPX integration using noop-ppx

Enhance test helpers:
- Normalize CRLF line endings in process output for Windows
- Support .bs.js artifacts in sandbox cleanup detection
- Add createCli, readFileInSandbox, writeFileInSandbox helpers
- Add OTEL config for build.parse_file and enriched compile_file spans
- Exclude noop-ppx from biome linting (CommonJS required)

Add tests for core build functionality:
- Build from a package subdirectory
- No stale artifacts on second build
- Filter flag to compile only matching modules

Add build error tests:
- Parse error reporting with file location
- Type error reporting
- Errors when a dependency module is deleted
- Circular dependency detection

Add module operation tests:
- File rename with and without dependents
- Duplicate module name detection
- Interface file compilation and error cases

Add namespace package tests:
- Build with namespace flag
- Namespace in compiler args
- File rename in namespaced package

Add dev-dependency tests:
- Dev source compiles with dev dependencies
- Non-dev source cannot use dev dependencies
- Clean removes dev source artifacts

Add build config tests:
- Experimental feature flags (valid, invalid key, invalid format)
- After-build hook execution (success and failure)
- Warning configuration in compiler args
- Warn-error CLI override
- Deprecated and unknown config field warnings

Add module system tests:
- CommonJS package with .bs.js suffix
- CommonJS in compiler args
- Suffix change triggers rebuild
- Duplicate package-spec suffix error

Add PPX integration tests using lightweight noop-ppx:
- PPX build produces output
- PPX flags in parser args
- PPX flags not in compiler args

Add JSX tests:
- JSX v4 build with @rescript/react
- JSX flags in parser args
- JSX preserve flag

Add tests for scoped clean, node_modules dependency cleanup,
and verifying no false compiler-update message after clean+rebuild.

Add format tests:
- Stdin formatting for .res and .resi
- Single file and all-files formatting
- Subdirectory-scoped formatting
- Check mode (pass and fail cases)

Add compiler-args tests:
- CWD invariance (same output from root and subdirectory)
- Warning flags in both parser and compiler args

Verify that a concurrent build is prevented while watch mode
holds the lock file.

Add watch mode tests:
- New file creation triggers compilation
- Warning persistence across incremental builds
- Config change triggers full rebuild
- Changes outside source dirs are ignored
- Missing source folder does not crash watcher
- Invalid config change recovery (watcher keeps running)
- File rename removes old artifacts and compiles new file
- File deletion removes artifacts

Tracing spans are thread-local, so compile_file spans created inside
Rayon's par_iter had no parent connection to the compile_wave span on
the main thread. Pass the wave span explicitly via `parent: &wave_span`
to establish the correct parent-child relationship.