Performance optimizations and expanded public API in earthdata-varinfo

[andreas-agouridis]

Description

This PR introduces several improvements to the earthdata-varinfo package, focusing on performance optimization, code quality, and API usability while maintaining full backward compatibility.

Key improvements include:

• Expanded public API exports in __init__.py for better usability and discoverability
• Performance optimizations through pre-compiled regex patterns in CFConfig
• Refactoring of VarInfo to use optimized helper methods
• Code quality improvements (e.g. proper regex raw string usage)

All existing unit tests pass successfully (122 tests, 234 subtests).

---

Jira Issue ID

N/A

---

Local Test Steps

1. Install dependencies and set up the environment
2. Run the full test suite:

   pytest

3. Verify all tests pass (122 tests, 234 subtests)
4. Optionally:

   * Test variable processing on large datasets to observe performance improvements
   * Import commonly used functions directly from `varinfo` to verify new exports

---

## PR Acceptance Checklist

* [ ] Jira ticket acceptance criteria met.
* [ ] `CHANGELOG.md` updated to include high level summary of PR changes.
* [ ] `VERSION` updated if publishing a release.
* [x] Tests added/updated and passing.
* [ ] Documentation updated (if needed).