refactor: drop dead code and refresh comments after the per-connection move

- Delete the now-unused CdpContext::new_full (its only caller switched to
  new_with_shared_context); have _new_inner build the shared BrowserContext and
  delegate, so the struct's field list lives in one place.
- Extract drive_module_eval, shared verbatim by load_module and
  load_inline_module.
- Update comments that still described the deleted process-wide V8 lock and the
  single-LocalSet model to the per-connection reality, drop the dangling
  reference to the removed obscura-js/src/v8_lock.rs, and soften the
  ISOLATE_CREATE_LOCK note now that the main-thread warmup is the real guard
  against the InitializeBuiltinJSDispatchTable segfault.

Refs #430.

crates/obscura-browser/src/page.rs

@@ -1308,7 +1308,7 @@ impl Page {
 
     /// V8 isolate handle for this page's runtime, if it has been initialized.
     /// Lets the CDP dispatcher arm a per-command watchdog (which bounds any one
-    /// command so a hung page cannot hold the process-wide V8 lock forever)
+    /// command so a hung page cannot hold this connection's V8 lock forever)
     /// without taking `&mut self`.
     pub fn isolate_handle(&self) -> Option<obscura_js::runtime::IsolateHandle> {
         self.js.as_ref().map(|js| js.isolate_handle())