test: enable coverage collection and thresholds

[mikesposito]

Explanation

Enabling Jest coverage collection and setting coverage thresholds.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Test configuration-only change; primary risk is CI failures or stricter test expectations due to enforced coverage thresholds and no-tests now failing.

Overview
Enables Jest coverage collection for the packages/snap workspace, including coverage output/reporters and global minimum coverage thresholds, while excluding index.ts files from coverage.

Updates the test script to run jest without --passWithNoTests, and refreshes the Snap snap.manifest.json source.shasum to match the rebuilt bundle.

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