Fix StateError during AOT execution by statically compiling injected client payload (#2804)

This PR resolves an issue where `webdev serve` crashes with a `StateError` when attempting to load `client.js` in AOT-compiled environments. 

**Root Cause:**
Previously, `DwdsInjector` relied on `Isolate.resolvePackageUri` to dynamically locate the `dwds` package on the file system at runtime. This fails within AOT snapshots because the injected client could not be resolved.

**Changes:**
- Bypassed the need for dynamic runtime file resolution by generating a statically compiled asset.
- Updated `tool/build.dart` to automatically bundle the transpiled `client.js` into a new `lib/src/handlers/injected_client_js.dart` file. The Javascript payload is encoded line-by-line using `jsonEncode` to preserve code readability.
- Refactored the `DwdsInjector` middleware to serve the statically guaranteed memory string.
- Added verification tests to enforce strict checksum equivalency between `client.js` file and generated `injected_client_js.dart`.

Related to https://github.com/dart-lang/webdev/issues/2761