Filter exception musd

[bergarces]

Explanation

MUSD is being filtered out when no occurrences are returned by tokens api.

References

Fixes https://consensyssoftware.atlassian.net/browse/ASSETS-3107

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
Very small, targeted change to token filtering logic with added tests; main risk is accidentally allowing similarly formatted asset IDs, but scope is limited to one hardcoded address.

Overview
Prevents the TokenDataSource EVM ERC-20 spam filter (minimum occurrences) from incorrectly hiding the specific mUSD token by adding an explicit allowlist exception for its contract address.

Adds coverage to ensure mUSD is retained even when occurrences is low or missing, and documents the fix in the assets-controller changelog.

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