Report BindingSpace trie trace diffs

[MesTTo]

Reports BindingSpace trie trace diffs.

The branch adds BindingSidecarPlan::explain_selected_trie_trace_diff. It compares the selected trie trace for two sidecar snapshots, keeps the execution reports separate, and returns a replay-shape diff only when both snapshots select the trie-backed kernel and both traces can be replayed.

Validation:

• cargo +nightly-2026-06-01 test -p mork --lib binding_plan with RUSTFLAGS='-C target-cpu=native'
• cargo +nightly-2026-06-01 test -p mork --lib with RUSTFLAGS='-C target-cpu=native'
• rustfmt --check on kernel/src/binding_plan.rs
• jscpd on kernel/src/binding_plan.rs, kernel/src/binding_space.rs, kernel/src/expression_trie.rs, kernel/src/pattern_relations.rs, kernel/src/test_exprs.rs, and kernel/src/test_sidecar_queries.rs
• git diff --check
• normal diffstat matched git diff -w --stat