Comprehensive enhancements to component how-to

[dotsdl]

This PR builds on @atravitz's component how-to (#667) by adding critical fixes and comprehensive enhancements.

🔴 Critical Fixes (Must Have)

These fix technical errors that would mislead users:

1. ✅ Fixed method names: Changed to_dict()/from_dict() to _to_dict()/_from_dict() (with underscores) - the actual method names
2. ✅ Added missing imports: First test example now includes all required imports (GufeTokenizableTestsMixin, pytest, Chem)
3. ✅ Fixed Sphinx references: Corrected :ref: syntax for proper cross-linking
4. ✅ Added serialization warning: Critical warning that custom attributes require implementing serialization methods
5. ✅ Added news entry: news/component-howto.rst per project requirements

🟢 Enhancements (Nice to Have)

These bring the guide to the comprehensive quality level of protocol.rst:

• Overview section (~28 lines): Explains Component characteristics and available base classes
• When to Create Custom Components (~18 lines): 5 practical use cases
• Enhanced Step 3 (~20 lines): Structured breakdown of required methods by inheritance scenario
• Using your Component (~33 lines): Complete working example showing full workflow
• Best practices and tips (~25 lines): 9 actionable recommendations
• Common pitfalls (~10 lines): 5 specific mistakes to avoid

📊 Stats

• Total additions: ~176 lines
• Final length: 269 lines (vs 125 in base)
• Structure: Matches docs/how-tos/protocol.rst quality

Integration Note

This PR incorporates your stylistic improvements from the latest commits:

• ✅ "it merely creates a new class identical to..." (Step 4 intro)
• ✅ "test all of your new features" (better phrasing)

Feel free to:

• Merge all changes
• Cherry-pick only the critical fixes
• Suggest modifications to any section

All changes have been reviewed to ensure they align with the project's documentation style.

---

Note: I've also posted the 5 critical fixes as individual review comments on the main PR #667 for reference.

[github-actions]

No API break detected ✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.79%. Comparing base (7aa3568) to head (776dfdc).

Additional details and impacted files

@@                  Coverage Diff                  @@
##           docs/component_howto     #716   +/-   ##
=====================================================
  Coverage                 98.79%   98.79%           
=====================================================
  Files                        40       40           
  Lines                      2492     2492           
=====================================================
  Hits                       2462     2462           
  Misses                       30       30           

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