Support strftime format expectation gallery metadata

[tarun-bandi]

Summary

Closes #12004.

This brings ExpectColumnValuesToMatchStrftimeFormat up to the supported expectation/gallery surface for the engines it already implements:

• adds gallery metadata, supported data source metadata, and schema extras
• declares Pandas and Spark support while documenting SQL as out of scope for now
• adds the generated schema file and includes the expectation in tasks.py
• expands integration coverage from Spark-only to Pandas + Spark while preserving the timezone-aware %z regression case

Validation

• PYTHONPYCACHEPREFIX=/Users/bandi/Documents/Codex/2026-07-24/new-chat/work/.pycache python3 -m py_compile great_expectations/expectations/core/expect_column_values_to_match_strftime_format.py tests/integration/data_sources_and_expectations/expectations/test_expect_column_values_to_match_strftime_format.py tasks.py
• python3 -m json.tool great_expectations/expectations/core/schemas/ExpectColumnValuesToMatchStrftimeFormat.json
• git diff --cached --check

I attempted to generate the schema through the local model import path, but this stripped workspace hit an unrelated SciPy/native import failure while importing the full expectation package.

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[joshua-stauffer]

hey @tarun-bandi, thanks for the PR. Looks like we're still missing a CLA from you, and there's another PR open for the same issue which is ready to merge. I'll close this now in favor of #12009, but would welcome a contribution in the future. Thanks!