Fix required configuration option cache invalidation

[Kryptonzy]

Summary

Make a configuration option reuse and track its derived .required() provider so configuration cache resets also invalidate the required view.

Fixes #954.

Root cause and approach

ConfigurationOption.required() created a detached provider each time. After that provider resolved a value, the original option had no reference to its cache. An override correctly reset the root/original option tree, but could not reach the required provider captured by a Singleton or Factory, so recreating the consumer still returned the stale value.

The original option now lazily creates and retains one required provider. reset_cache() cascades to that provider, deepcopy preserves the relationship, and calling required() on an already-required option is idempotent. This keeps the existing cache for performance, as requested in the issue discussion, instead of recomputing every access.

Verification

• New regression on unmodified code: failed because the recreated singleton received {"value": "initial"} during the override.
• .venv/bin/pytest -q tests/unit/providers/configuration/test_config_py2_py3.py::test_required_cache_is_reset_after_option_override — 1 passed.
• .venv/bin/pytest -q tests/unit/providers/configuration — 204 passed.
• Related Singleton, Factory, and deepcopy test groups — 328 passed.
• The Cython extension was rebuilt successfully before the green test runs.
• The changed Python test file passes Flake8; git diff --check passes. (providers.pyx is Cython and is not directly parseable by Flake8.)
• The remote Tests and linters workflow is currently action_required and generated no jobs. This is the repository's approval gate for workflows from forks, not a test execution failure; no remote-green result is claimed before a maintainer approves it.

Scope

The change is limited to ConfigurationOption cache linkage/copying and one focused regression. It does not remove caching, change configuration lookup rules, or alter Singleton/Factory behavior.

AI assistance

OpenAI Codex (GPT-5) was used to investigate the cache lifecycle, implement the focused change and regression, rebuild the extension, and run/review the verification above. I reviewed the final diff and am disclosing this assistance explicitly.

[coveralls]

coverage: 92.402%. remained the same — Kryptonzy:agent/fix-configuration-option-cache-override into ets-labs:develop

[ZipFile]

Not exactly fond of this solution, but given that we have to keep backward compatibility this is probably good enough one. For v5 we have to rethink config management for sure.