Expose public API entry points from native classes

[adamziel]

What it does

Adds the native extension class layer that the PHP integration PR can bind to directly.

This PR now implements the public entry points in Rust instead of leaving PHP wrappers to fill behavior back in:

• WP_HTML_Native_Tag_Processor::next_tag() accepts the public string|array|null query shape, including tag_name, class_name, match_offset, and tag_closers.
• WP_HTML_Native_Processor::next_tag() accepts public tag, class, match-offset, and breadcrumb queries.
• WP_HTML_Native_Processor::normalize() and serialize() run through native serialization instead of calling back into the public PHP class, avoiding recursion once the public PHP class resolves to the native implementation.
• WordPress\XML\NativeXMLProcessor::next_tag() accepts the public local-name, namespace/local-name, match-offset, and namespaced breadcrumb query shapes.
• WordPress\DataLiberation\URL\NativeURLInTextProcessor::get_parsed_url() delegates to WPURL::parse() so callers receive the component URL object surface instead of a placeholder string.
• URL-in-text filtering runs in Rust: base-protocol handling, HTTP(S) filtering, credential rejection, public-suffix checks for bare domains, invalid-port rejection, and replacement conflict handling.
• Adds a Native APIs GitHub Actions workflow that builds the PHP extension, loads it, and runs extensions/native-apis/tests/verify-native-apis.php.

Rationale

The stacked PHP PR should only decide whether to expose native or PHP implementations. If public behavior lives in PHP wrapper classes, reviewers have to audit two implementations and the wrappers grow into a second parser layer.

This PR moves the public API burden into the extension so the next PR can use empty native subclasses plus fallback loaders.

Implementation

The native classes expose a supports_public_api() marker. PHP loaders in the next PR use that marker to avoid stale extension builds that do not support this public surface.

The verifier now covers representative public calls:

$processor->next_tag( array( 'tag_name' => 'p', 'class_name' => 'target' ) );
$html->next_tag( array( 'breadcrumbs' => array( 'ARTICLE', 'IMG' ) ) );
$xml->next_tag( array( 'breadcrumbs' => array( array( 'https://wordpress.org', 'item' ) ) ) );
$url->get_parsed_url()->hostname;

Native HTML serialization normalizes opening-tag attributes from the original source bytes, preserving first-duplicate-wins behavior while quoting unquoted values and retaining boolean attributes.

Unsupported factory options still return null for now, keeping native opt-in conservative while the public surface is filled in.

Testing instructions

Local checks run:

cd extensions/native-apis
cargo fmt && cargo test
php -l extensions/native-apis/tests/verify-native-apis.php
bash -n extensions/native-apis/build-extension.sh
/home/claude/php-toolkit/vendor/bin/phpcs -d memory_limit=1G /tmp/php-toolkit-public-api/extensions/native-apis/tests/verify-native-apis.php
git diff --check

Local limitation: this machine does not have php-config, so cargo check --features php-extension cannot run locally. The new Native APIs / Build and verify PHP extension workflow is the required extension build/load check for this PR.