Optimize traffic to the chrome debug target

Possible related to #975, I notice that the package:dwds implementation makes more calls to the underlying chrome debug target than is necessary. For example, the implementation of `_getScript(()` (in `inspector.dart`) makes backend calls, irrespective of whether we've already populated information about the script before.

I think it would be valuable to audit the typical log of calls to the chrome debug target over a debug session, and see if there is any opportunity for caching of data, or other optimization.

cc @grouma

Start in package:dwds, especially inspector.dart and the _getScript implementation. Capture and audit a typical debug-session log of calls to the underlying Chrome debug target, then determine whether previously populated script information can avoid repeated backend calls. Done means identifying and applying justified caching or another call-reduction optimization.

Written by the indexing model from the issue text.