Typeset block $$…$$ math in display style, not text style

[manemajef]

Summary

• add an explicit inline/display mode to LaTeX rendering while preserving the existing mode-less renderer API
• route block math as display and body/table math as inline
• map the mode to SwiftMath labelMode and include it in memory and disk cache keys
• keep mode-less SwiftMath calls in text style

Root cause

The parser and layout already distinguished inline and block math, but both styling paths passed only delimiter-free content through LatexRenderer. SwiftMathBridge therefore had no mode information and forced every formula into text style.

Compatibility

Existing LatexRenderer conformers can continue implementing only the original method. The new mode-aware requirement has a default implementation that forwards the same delimiter-free content to that method.

Validation

• DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer swift test --filter LatexRenderModeTests
• DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer swift test
• 322 tests passed across 58 suites

[manemajef]

Superseded by #153 — same change, rebased onto current main, with the test-target split and protocol defaults cleaned up.