Simplify replay refactor cleanup

[Jud]

Summary

• share the lineup squash current-index adjustment between replay and rule shadow state
• replace the pending BIP run snapshot tuple with a named struct
• remove a misleading unused substitution parameter and avoid repeated base occupancy lookups

Validation

• cargo +1.95.0 fmt --check
• cargo +1.95.0 clippy --all-targets -- -D warnings
• cargo +1.95.0 test --all-targets
• cargo +1.95.0 test --doc
• RUSTDOCFLAGS='-D warnings' cargo +1.95.0 doc --no-deps
• cargo +1.95.0 package --allow-dirty