fix: toolbox search final trigram

[goughjo02]

The basics

• [x] I validated my changes

The details

Resolves

Fixes https://github.com/RaspberryPiFoundation/blockly-samples/issues/2645

Proposed Changes

• Include the final trigram when generating search tokens to prevent partial matches on long queries.
• Add a regression test covering the “conso” false positive case.
• Expand BlockSearcher tests for short/empty input, underscore normalization, dropdown alt text indexing, and disambiguation between similar blocks.

Reason for Changes

• Prevent toolbox search from returning false positives for queries longer than three characters and improve overall search accuracy.

Test Coverage

• npm test -- --runInBand (blockly-scripts test)

Documentation

• No documentation updates needed.

Additional Information

• Additional tests define temporary blocks/dropdowns to exercise edge cases; no user-facing behavior changes beyond correcting search results.

[gonfunko]

Thank you for identifying and reporting this issue and sending a fix! I really appreciate the improved tests as well. I just had two minor questions, and if you could run npm run format and commit the results of that to make the linter happy I think we should be good to merge this.