fix(parser): Protect inline code from formatting while allowing spans

[joshdoman]

This fixes issue #2. Previously, links, bold, and italic HTML was sometimes incorrectly applied to inline code containing a special character. For example, __init__ should not be bolded, but it currently is.

At the same time, formatting that spans across inline code should still be applied. The fix is to replace code blocks with a unique placeholder that is unlikely to appear in the text.

This PR replaces each code block with indexed private use area unicode (\uE000{index}\uE001) and then applies link, bold, and italic formatting. When finished, the placeholder is replaced with the corresponding code block.

(The PR includes comprehensive test coverage for edge cases including nested formatting, multiple code blocks, and complex spanning scenarios)

Before:

After:

---

Summary by cubic

Protects inline code from being formatted while still allowing bold/italic/link spans across code. Fixes incorrect styling like init being bolded inside code (fixes #2).

• Bug Fixes
  • Wraps each rendered code block in a unique Private Use Area placeholder, parses links/bold/italic, then restores the code block.
  • Blocks formatting inside code but preserves formatting that spans across code segments.
  • Adds tests for nested formatting, multiple code blocks, and spanning scenarios.