fix: correct disjoint union contract execution

[bennyhodl]

Summary

Later branches of a disjoint-union contract could use CETs or adaptor signatures from an earlier branch. This change lets each event settle the contract when its own oracle threshold is met.

Changes

• Use each branch's CET range for signing and verification. Apply the correct CET and adaptor-signature offsets during manager settlement.
• Preserve the offer's CET locktime on later branches.
• Check later events when independent enum events share an outcome label. Preserve oracle indexes during maturity checks and sort attestations by announcement index.
• Continue to later branches when oracle responses do not give a usable outcome.
• Add a baseball contract with separate 2-of-3 oracle groups for two hits, numerical at-bats, and a team win. Test each branch from both parties through the stateless and manager APIs.

The locktime correction changes CET reconstruction for older multi-event messages. Those messages need legacy handling. Channel settlement and metadata that exposes only the first event remain separate work. The details are in docs/disjoint-union.md.

Testing

Validation completed during implementation:

• All 33 stateless tests and 56 manager unit tests passed.
• All 20 baseball regtest cases passed. The six automatic cases also passed with NB_CONFIRMATIONS=6.
• The existing mixed enum/numerical regtest with oracle disagreement support passed.
• The manager build without default features passed. Targeted Clippy checks with --no-deps and -D warnings passed.
• Changed Rust files passed rustfmt. The branch diff passes git diff --check.

Clippy with dependency checks reports an existing explicit_counter_loop warning in kormir/src/storage.rs on Rust 1.98.