Precompile client-side scripts for V8

While has some functional relation to #33 - that issue is about scripts provided by Gost.

This is about scripts referenced by the application;

When encountering a `` element, precompile the script the first time it's fetched, respecting cache control headers.

Every test for the same web application is extremely likely to include the same scripts, e.g., every single HTMX app test would include HTMX.

Precompiling should provide a significant performance boost for larger test suites.

Start at the code path that handles application-referenced elements and fetches their contents. Trace how cache-control headers are exposed, then determine where first-fetch precompilation can be reused for later tests of the same web application. Done means eligible scripts are precompiled once while cache-control behavior is respected, with coverage for repeated script fetches.

Written by the indexing model from the issue text.