Add BindingSpace trie join sidecar

[MesTTo]

Adds a trie-backed BindingSpace join sidecar.

The branch adds trie_join, TrieJoinResult, and TrieJoinStats over positive BindingSpace rows. It rekeys each input relation by the requested variable order, traverses synchronized sorted domains, and exposes BindingSidecarPlan::execute_trie_join for arrangement-backed sidecar plans. The regressions compare trie output against the existing Generic Join oracle and the current product-query path.

Validation:

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