feat: bsc integration

[ramizhasan111]

Pull Request

Closes: PRO-xxxx

Summary

Please include a succinct description of the purpose and content of the PR. What problem does it solve, and how? Link issues, discussions, other PRs, and anything else that will help the reviewer.

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Checklist [feel free to add/remove/edit as appropriate but please don't ignore]

Before marking this as ready for review, consider the following:

• The PR is complete:
  • Scope is clear and fully implemented.
  • Tests:
    • Unit tests for isolated local conditions.
    • Proptests for important invariants.
    • Integration tests for runtime-wide behaviours.
    • Bouncer tests for E2E features involving external chains.
  • Benchmarks: did you leave any dangling placeholders?
  • Migrations: if you wrote one, did you test it using try-runtime?
  • Bouncer typegen: if you changed any runtime types you might need to update this.
• Make life easy for the reviewer:
  • Intended behaviours are clear and, where possible, covered by tests.
  • Unrelated changes are isolated in dedicated commits.
  • Interfaces are clearly documented.
  • Anything non-obvious is documented in the Summary section above.
• Consider asking an AI for a local review to catch any embarrassing mistakes early.
• Vice-versa: read your code carefully to ensure no AIs added anything embarrassing.

[codecov]

Codecov Report

❌ Patch coverage is 27.29234% with 674 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../runtime/src/chainflip/witnessing/bsc_elections.rs	19%	186 Missing ⚠️
engine/src/witness/bsc_elections.rs	0%	101 Missing ⚠️
state-chain/chains/src/bsc/api.rs	24%	90 Missing and 6 partials ⚠️
state-chain/chains/src/bsc.rs	10%	61 Missing ⚠️
state-chain/chains/src/address.rs	0%	21 Missing and 1 partial ⚠️
state-chain/runtime/src/runtime_apis/impl_api.rs	0%	22 Missing ⚠️
state-chain/node/src/chain_spec.rs	64%	21 Missing ⚠️
engine/src/state_chain_observer/sc_observer.rs	5%	20 Missing ⚠️
...in/runtime/src/chainflip/address_derivation/bsc.rs	0%	20 Missing ⚠️
engine/src/lib.rs	0%	18 Missing ⚠️
... and 22 more

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