landlock: Optimize coalesced hash table lookup performance

[Copilot]

Performance optimizations for the flat array domain's coalesced hash table lookup path.

Changes

• Force inlining: Apply __always_inline to all hot path functions (h_find, dom_index_hash_func, landlock_domain_find, generated accessors in DEFINE_COALESCED_HASH_TABLE)

• Branch hints: Add likely()/unlikely() annotations:

  • Fast path element comparison
  • Empty table check
  • Zero hash_bits edge case

• Early termination: Skip collision chain traversal when element at hash position doesn't belong there—indicates no matching element exists

• Bounds checking: Add WARN_ON_ONCE guard in collision chain traversal

// Early termination: avoid traversing chains that can't contain our element
if (hash_elem(curr_elem, table_size, hash_bits) != target_hash)
    return NULL;

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