feat(tron-wallet-snap): remove assets migration feature-flag routing - #97

## Explanation

This PR extends the Snap’s transaction handling by introducing a
`TransactionMapper` that classifies/massages Horizon on-chain
transactions into MetaMask keyring transaction shapes
(send/swap/change-trust/receive), while also standardizing keyring
“asset” payloads to include `unit`, `amount`, and `fungible` fields and
adding some supporting formatting utilities/constants.

**Changes:**
- Added `TransactionMapper` (+ tests + Horizon fixtures) to map Horizon
transactions into keyring transactions and to skip dust payments.
- Expanded transaction utilities with operation/transaction-type
detectors (swap/receive/change-trust/dust/status helpers).
- Standardized keyring transaction request `asset` shapes and added a
shared `removeTrailingZeros` helper (plus tests) and a dust-amount
constant.

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## References

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## 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](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them