feat: enable BFA funding in Lightning RGB wallets

[bandrivskiy]

BFA channel funding is rejected by the internal Lightning RGB wallet because BFA is missing from its supported schemas and the funding acceptor opens the wallet without an Ethereum RPC endpoint.

Read the optional Ethereum RPC endpoint from the Lightning KV store, enable BFA when it is configured, and pass it to rgb-lib when accepting funding consignments. A shared schema selector keeps node and Lightning wallets consistent, including IFA's mainnet restriction. Missing or empty endpoints preserve the existing behavior for wallets without BFA.

Use the released rgb-lib tag v0.3.0-beta.50-bfa in both lightning and lightning-invoice. It includes the merged BFA metadata validation fix from rgb-lib#113. Includes unit tests for legacy/disabled endpoint configuration and schema selection.

Companion node integration: rgb-lightning-node#205.

Validation:

• Includes the latest fetched rust-lightning/dev (fc5c4c64d).
• Cargo metadata resolution with electrum/esplora and the companion node's BFA dependency patches confirms both crates use the single v0.3.0-beta.50-bfa source (1b951af0).
• The release tag has the same complete Git tree as the previous rgb-lib pin (4d65421), which passed cargo check --locked --features uniffi,vls,vss,test-utils --all-targets through the companion node. Compilation was not repeated for this tag-only update.
• The BFA regtest/Anvil lifecycle passed with the earlier rgb-lib fix (840e22a): channel funding, multihop payments, restart, cooperative and force close, and an on-chain burn. The lifecycle has not been rerun with the release tag.
• Formatting of the changed Rust module passed previously; git diff --check passes with this update. The new LDK unit tests have not been run separately.

Standalone CI was already failing on dev: the Ubuntu build log shows Cargo cannot resolve the yanked secp256k1 0.32.0-beta.2 dependency. The companion node supplies its existing pinned BFA dependency patches; this PR does not change standalone dependency resolution or CI configuration.