Extend API doc auto-linker for class bases, re-exports, and module labels

[Copilot]

This stacks on the docstring auto-linker work and closes remaining link gaps in generated API pages. It makes class inheritance and re-export entries linkable when symbols resolve in the index, while preserving plain code spans for external/unresolvable symbols.

• Class Bases: line now participates in symbol linking

  • render_class now formats bases via a dedicated _format_bases() path.
  • Each base is rendered independently and passed through _rewrite_symbol_refs, so internal PyRIT bases become MyST links and external bases stay plain.

• ## Re-exports now links alias and target consistently

  • Added _format_reexport_alias():
    • first tries module-qualified lookup ({module}.{alias}) so aliases resolve to their own page anchor when available;
    • falls back to short-name rewriting when no module-qualified entry exists.
  • Added _format_reexport_target() to route targets through _rewrite_symbol_refs, linking resolvable FQNs and leaving external paths unchanged.

• Module frontmatter now includes a stable page label

  • render_module now emits label: api-<module_slug> alongside short_title, enabling page-level cross-reference targets.

• Unit coverage expanded for new link behavior

  • Added targeted tests for:
    • mixed internal/external base rendering,
    • re-export alias preferred module-qualified resolution,
    • re-export alias fallback behavior,
    • module frontmatter label emission.

# Before
Bases: `PromptTarget`

# After
Bases: [`PromptTarget`](#api-pyrit_prompt_target-PromptTarget)

[romanlutz]

@ValbuenaVC this seems related to #1824