[core] Reject overlapping partial-update sequence groups

[reswqa]

Purpose

Rust currently accepts fields.<ordering-fields>.sequence-group definitions whose ordering fields overlap across different groups, e.g. fields.s.sequence-group=a together with fields.t,s.sequence-group=b. Ownership of the shared ordering field is then ambiguous, and which group's comparator governs it is an accident of option iteration. btw, Java rejects such configurations with error message.

Brief change log

• rejects such configurations in validated_sequence_groups.

Tests

• New unit test covers containment (s vs t,s), partial overlap (a,b vs b,c) and permuted duplicates (a,b vs b,a), asserting the error names the shared field and both option keys.
• cargo test -p paimon passed. Related integration suites passed.
• cargo fmt -p paimon -- --check and cargo clippy -p paimon --all-targets --features fulltext,vortex -- -D warnings pass.

API and Format

No API or storage format changes.

Documentation

No Rust doc change.