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/languages/pygrep.py

@@ -96,8 +96,12 @@ def run_hook(
         is_local: bool,
         require_serial: bool,
         color: bool,
+        pass_filenames_via_stdin: bool = False,
 ) -> tuple[int, bytes]:
     cmd = (sys.executable, '-m', __name__, *args, entry)
+    if pass_filenames_via_stdin:
+        stdin = lang_base.to_nul_delimited_filenames(file_args)
+        return xargs(cmd, (), color=color, input=stdin)
     return xargs(cmd, file_args, color=color)
 
 
@@ -116,6 +120,11 @@ def main(argv: Sequence[str] | None = None) -> int:
     parser.add_argument('filenames', nargs='*')
     args = parser.parse_args(argv)
 
+    if not args.filenames:
+        stdin = sys.stdin.buffer.read()
+        if stdin:
+            args.filenames = lang_base.from_nul_delimited_filenames(stdin)
+
     flags = re.IGNORECASE if args.ignore_case else 0
     if args.multiline:
         flags |= re.MULTILINE | re.DOTALL