fix: honor ordered list start number

[yyq1025]

What/Why?

Fixes #524.

Per CommonMark/GFM, the start number of an ordered list is determined by the list number of its first item — 3. foo should render as 3, 4, 5 (see https://spec.commonmark.org/0.31.2/#start-number). md4c already reports this via MD_BLOCK_OL_DETAIL.start, but the shared parser dropped it, so both renderers restarted every ordered list at 1.

This PR passes it through as a start attribute on the OrderedList node (set only when != 1, so renderers can treat absence as the default) and seeds the per-level item counter from it on iOS and Android. 0. start is honored too, matching GitHub rendering. Nested-list numbering is unaffected — the counter stack works exactly as before, each level just starts from its own first item's number.

Scope note: the standalone android-enriched-markdown package is intentionally untouched — its renderer ignores the new attribute, so behavior there is unchanged. Happy to mirror the fix in a follow-up if useful.

Testing

Added ordered_list_start_test.yaml (basic/block_elements) with iOS + Android screenshot baselines, captured via --update-screenshots and verified to assert clean afterwards. Existing ordered_list_test and nested_ordered_list_test still pass on both platforms (lists starting at 1 render exactly as before — the attribute isn't emitted for them).

Screenshots

Input:

3. Add eggs and vanilla extract
4. Pour into a greased tin
5. Bake for 30 minutes

iOS	Android

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)

🤖 Generated with Claude Code

[eszlamczyk]

Hi, thanks for the quick well done job! Im gonna remove some comments and merge so we get this in next nightly release!