Add B² Network mainnet support

[a10zn8]

Summary

• Bump emerald-grpc and pkg/chains/public submodules to add-bsquared tips.
• Regenerated pkg/dshackle/common.pb.go.
• pkg/chains/chains_data.go is generated at build time via make generate-networks.
• B² Network mainnet (chain-id 223 / 0xdf, grpcId 1158) — OP Stack Bitcoin L2.

Verification

• make dshackle-proto-gen && make generate-networks && go build ./... passes.

Companion PRs

• emerald-grpc: Add CHAIN_BSQUARED__MAINNET constant emerald-grpc#155
• public: Add B² Network mainnet public#218
• dproxy: https://github.com/drpcorg/dproxy/pull/2547
• dshackle: Add B² Network mainnet support dshackle#826
• nodecore: Add B² Network mainnet support #180
• infra: https://github.com/drpcorg/infra/pull/4644

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