fix: remove global network reference in bridge allowance handler

[SteP-n-s]

Explanation

Updates logic of getBridgeERC20Allowance method to use chainId parameter to retrieve the networkClient.

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, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

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Note

Update getBridgeERC20Allowance to fetch the network client by chainId; add error handling/tests and update changelog.

• BridgeController:
  • Add #getNetworkClientByChainId(chainId) to resolve client via NetworkController:findNetworkClientIdByChainId then getNetworkClientById.
  • Update getBridgeERC20Allowance to use #getNetworkClientByChainId instead of the selected network; throw on missing client/provider.
• Tests (src/bridge-controller.test.ts):
  • Adjust mocks to expect findNetworkClientIdByChainId → getNetworkClientById call sequence.
  • Add cases for missing network client and missing provider errors.
• Docs:
  • Update CHANGELOG.md under Unreleased with the fix entry.

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