add pass_filenames_via_stdin for large changesets

pre-commit currently passes selected filenames to hooks via argv.
For large changesets (or --all-files), argv length limits are hit and
filenames are partitioned, causing multiple hook invocations.

This means there is currently no built-in way to pass filenames to an
underlying hook in one shot without chunking / re-running. The only practical
workaround is to set pass_filenames: false and run custom git operations in
hook code to reconstruct the file set, which is expensive and duplicates
pre-commit's own file-selection logic.

This change adds a hook option:

    pass_filenames_via_stdin: true

When enabled, pre-commit sends filenames as NUL-delimited bytes on stdin and
runs the hook in a single invocation (no argv chunking).

Why NUL-delimited stdin:
- safe for filenames containing spaces/newlines
- matches established -0 conventions in unix tooling

Usage for hook authors:
- shell:

    while IFS= read -r -d '' filename; do
        ...
    done

- python:

    data = sys.stdin.buffer.read()
    filenames = [os.fsdecode(p) for p in data.split(b'\0') if p]

Behavior notes:
- default remains argv-based passing
- pass_filenames: false still disables filename passing entirely

Implementation includes schema/runtime wiring, shared NUL encode/decode
helpers, and tests covering defaulting and runtime behavior.

pre_commit/util.py

@@ -92,6 +92,7 @@ def cmd_output_b(
         check: bool = True,
         **kwargs: Any,
 ) -> tuple[int, bytes, bytes | None]:
+    input_data = kwargs.pop('input', None)
     _setdefault_kwargs(kwargs)
 
     try:
@@ -104,7 +105,7 @@ def cmd_output_b(
         except OSError as e:
             returncode, stdout_b, stderr_b = _oserror_to_output(e)
         else:
-            stdout_b, stderr_b = proc.communicate()
+            stdout_b, stderr_b = proc.communicate(input_data)
             returncode = proc.returncode
 
     if check and returncode: