Add rise and fadeAndRise paragraph animation styles

[Jun Yan (junyan72)]

Summary

Adds vertical-offset ("rise") streaming animations alongside the existing fade, by generalizing the paragraph animation engine so its per-frame mutation is pluggable. This is a step toward character-level streaming animation.

• Add ParagraphAnimationStyle enum (.fade, .rise, .fadeAndRise) plus rise/wave constants in ParagraphAnimation.swift.
• Expose paragraphAnimationStyle on MarkdownRenderConfig with a withParagraphAnimationStyle(value:) builder (defaults to .fade, so existing behavior is unchanged).
• Generalize updateTextViewWithCurrentAnimations() in ParagraphUIView and ParagraphNSView to apply foreground-color alpha (fade) and/or .baselineOffset (rise) per range.
• Animate rise per composed-character sequence with a continuous, capped stagger (delayBetweenCharacters, maxWaveLead) so glyphs ripple in instead of whole words moving as rigid blocks. Added splitIntoCharacters(withIn:).
• Thread the style through both SwiftUI wrappers and demo .fadeAndRise in the sample app.

Note: intrinsic size is kept cached during animation, so surrounding blocks don't reflow; a negative baselineOffset can slightly clip descenders (tunable via riseDistance). Pure .fade still uses the original per-word path.

This does not yet implement the buffered "release one grapheme at a time" sequential mode described in the issue.

Refs #149

Validation

• swift build — succeeds (only pre-existing deprecation warnings).
• swiftlint --strict on the changed files — clean.
• make generate-sample-project — regenerates the sample app project.
• Manual verification in the sample app with .fadeAndRise.

OSS readiness

• No secrets, internal URLs, private identifiers, or product-only service names were added.
• Public docs, fixtures, or notices were updated if behavior or dependencies changed. (new public API is documented inline; default behavior unchanged)
• Third-party dependency changes (adds, removes, version bumps) are intentional and reviewed. (no dependency changes)
• Streaming/incomplete markdown behavior remains covered by fixtures or tests. (no automated tests added yet for the new styles)