gsutil compiled crcmod noty detected on macos

`gsutil help crcmod` says on macos gsutil should come with crcmod precompiled and to open a support request when the auto-detection fails.

Here is my `gsutil version -l` output:

```
gsutil version: 5.35
checksum: 463ae9998133cda1b7d55035f3d5e7b9 (OK)
boto version: 2.49.0
python version: 3.12.12 (main, Oct 9 2025, 11:07:00) [Clang 17.0.0 (clang-1700.3.19.1)]
OS: Darwin 25.0.0
multiprocessing available: True
using cloud sdk: True
pass cloud sdk credentials to gsutil: True
config path(s):
gsutil path: /opt/homebrew/share/google-cloud-sdk/bin/gsutil
compiled crcmod: False
installed via package manager: False
editable install: False
shim enabled: False
```

Start with `gsutil help crcmod` and reproduce the report using `gsutil version -l` on macOS. Trace how gsutil determines whether compiled crcmod is available, then compare that result with the documented expectation. Done means the detection accurately reflects the installed crcmod state or the supported macOS behavior is clearly documented.

Written by the indexing model from the issue text.