feat(vscode): update snippets to match latest signals.dart version

[google-labs-jules]

This change updates the VS Code extension to match the latest version of the signals.dart package. It adds new snippets for persistedSignal, the $ extension, trackedSignal, and lazySignal, and removes the deprecated ValueSignal snippet. It also updates existing snippets to reflect the latest changes in the package. This will improve developer productivity by providing up-to-date code snippets for the latest features in the signals.dart package.

Fixes #387

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PR created automatically by Jules for task 10410728845207246398 started by @rodydavis

[google-labs-jules]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.28%. Comparing base (14c0fa9) to head (e0ef856).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #429      +/-   ##
==========================================
- Coverage   64.42%   64.28%   -0.15%     
==========================================
  Files          87       88       +1     
  Lines        2145     2167      +22     
==========================================
+ Hits         1382     1393      +11     
- Misses        763      774      +11     

see 1 file with indirect coverage changes

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[rodydavis]

@jules add all the signals from signals_core, signals_hooks, signals_flutter

Docs: https://dartsignals.dev/llms.txt

[google-labs-jules]

@jules add all the signals from signals_core, signals_hooks, signals_flutter

Docs: https://dartsignals.dev/llms.txt

I have updated the snippets to include all the signals from signals_core, signals_hooks, and signals_flutter as you requested.