fix: whitespaces parsing inside normalizer

[kacperzolkiewski]

Summary

This PR fixes whitespaces parsing between tags in normaliser.

Test Plan

Insert some external html into example mobile/web app by Set input's value button for example:

<p>Asdasd</p>
<p>Asdasd</p>
<p>Asdasd</p>

And see if the output html is the same.

Screenshots / Videos

Screen.Recording.2026-07-16.at.12.48.12.mov

Compatibility

OS	Implemented
iOS	✅
Android	✅
Web	✅

Checklist

• E2E tests are passing
• Required E2E tests have been added (if applicable)

[Copilot]

Pull request overview

This PR addresses an HTML normalization issue where whitespace-only text nodes between block elements (e.g., pretty-printed \n between <p> tags) could be treated as meaningful inline content, leading to empty paragraphs and later extra <br>s during serialization.

Changes:

• Add “whitespace-only buffer” detection and discard inter-block whitespace during inline paragraph flushing.
• Adjust <br> handling in mixed inline/block runs to avoid generating empty paragraphs from layout whitespace.
• Add regression tests for inter-block whitespace normalization in both the web (TS) and native (C++) paths.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/web/normalization/htmlNormalizer.ts	Discards whitespace-only buffered inline content to prevent empty <p> output and extra <br>s.
src/web/__tests__/htmlNormalizer.test.ts	Adds regression coverage for pretty-printed inter-block whitespace cases.
cpp/tests/GumboParserTest.cpp	Adds equivalent regression coverage for the C/C++ normalizer path.
cpp/parser/GumboNormalizer.c	Implements whitespace-only detection and attempts to discard inter-block whitespace during normalization.

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[hejsztynx]

Works great! Just left some minor comments.