ENG-469 Stabilize integration suites: Electrum skips, retries, env RPC, keep-common bump

[piotr-roslaniec]

Summary

• Skip the offline testnet Electrum WSS endpoint (TODO 3843) across all Electrum integration subtests.
• Increase retry window for public electrs-esplora endpoints to reduce timeouts.
• Refresh sepolia peer expectations to match embedded defaults.
• Require ETHEREUM_MAINNET_RPC_URL for the block timestamp integration test and pass it into CI.
• Avoid transaction decoding in Ethereum block lookup by using headers (fixes “transaction type not supported”).
• Bump keep-common to latest (commit e822118…) to align with header-based block fetch.

Testing

• go test ./config
• go test -tags=integration ./pkg/bitcoin/electrum # WSS skipped, electrs retries extended
• go test -tags=integration ./pkg/chain/ethereum # with ETHEREUM_MAINNET_RPC_URL set
• go test -v ./pkg/tbtcpg/internal/test

[linear]

ENG-469 Fix `transaction type not supported`