Security audit fixes: fn() whitelist, escaping, and performance (v0.1.4)

- WooCommerceExtension: ALLOWED_FUNCTIONS whitelist for fn() Twig function
- Notice templates: data attributes use wp_kses_post instead of raw
- Search form: esc_attr on search query value attribute
- Per-request ContextBuilder caching via static variable
- Shared wc_bootstrap_render_in_page_shell() helper (DRY)
- Removed unused WC_BOOTSTRAP_VERSION and WC_BOOTSTRAP_URL constants

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/notices/error.html.twig

@@ -23,7 +23,7 @@
         {% else %}
             <ul class="mb-0 ps-3">
                 {% for notice in notices %}
-                    <li {{ notice.data|default('')|raw }}>
+                    <li {{ notice.data|default('')|wp_kses_post }}>
                         {{ notice.notice|raw }}
                     </li>
                 {% endfor %}