fix: better list children rendering logic

[eszlamczyk]

What/Why?

Fixes #243 — lists containing block children (fenced code blocks, nested sublists) rendered broken: markers
were lost or drawn inside code blocks, checked-task strikethrough bled across code, and code blocks ignored
list indentation.

Root cause: list styling was applied post-hoc — children rendered list-ignorant, then ListItemRenderer
stamped indent/marker metadata over the result, which broke whenever an item's first child wasn't plain text.
This PR moves list layout to a top-down model:

Shared parser (packages/core/cpp)

• wrapListItemInlineRuns post-pass: md4c emits bare inline children for tight list items; they're now wrapped
  in synthetic Paragraph nodes (marked tight), so renderers only ever see block children. One change covers
  iOS, Android (JNI) and web (rebuilt md4c.js; web renderers needed no changes).

iOS

• BaseRenderer is now a template method (renderNode: = snapshot scope → renderNodeContent: → restore).
  RenderContext.snapshotScope/restoreScope replaces the per-renderer @try/@finally partial restores and stops
  block-style state leaking between sibling blocks.
• RenderContext.accumulatedIndent: ListItemRenderer pushes the item indent around its children;
  CodeBlockRenderer folds it into its paragraph style and CodeBlockBackground insets the background rect —
  code blocks in list items now render indented under the item content (CommonMark behavior).
• Markers are self-contained ENRMListMarkerDescriptors planted on the item's first content character
  (appending when one already exists). ListMarkerDrawer draws every descriptor at its own gutter — fixes
  missing markers on code-block-first items, draws both markers (browser-style) for sublist-first items, and no
  longer duplicates markers per paragraph in loose items.

Android (mirror)

• BlockStyleContext.accumulatedIndent → CodeBlockSpan.leadingIndent (leading margin + background inset).
• BaseListSpan split into segments around code blocks (keeps the metric-affecting span off code text), single
  drawsMarker owner per item; when the item starts with a code block/sublist, a zero-margin
  ListMarkerAnchorSpan draws the marker instead.
• applyCheckedDecorations excludes code-block ranges — no more strikethrough across code in checked tasks;
  inline-code backgrounds and line-height spans are list-margin aware.

Not in scope (pre-existing): ordered-list start is ignored by the parser (1. + nested 2. x renders 1. 1. x).

Testing

• e2e suites green on both platforms; targeted re-run: yarntest:e2e:mobile --include-tags list,code_block,task_list.
• 5 new e2e fixtures: loose/tight list×code-block combos, code-block-first items, sublist-first item, checked task containing a code block (previously uncovered bug class).
• Manual verification via example app (screenshots) (edge cases mirrored from the fixtures).

Screenshots

Before	After

PR Checklist

• Code compiles and runs on iOS
• Code compiles and runs on Android
• Updated documentation/README if applicable
• Ran example app to verify changes
• E2E tests are passing
• Required E2E tests have been added (if applicable)