harness: correct Wasmtime instantiation verdicts and diagnostics

[lannbot]

Summary

• Correct instantiation verdicts: recognize native start traps and narrowly typed host-resource import mismatches; reject wrong-phase errors and check link diagnostics.
• Report actual variant discriminants and case counts in memory/flat lifting. The Wasmtime assertion passes through ordinary matching, with no file/revision-specific exception.
• Recognize verified resource-borrow and string-alignment diagnostic equivalents; remove seven stale failure expectations.
• Record declared-import checking constraints in the plan contract's open items. Full declared-import checking remains follow-up work under testing: triage classified Wasmtime supplementary coverage gaps #372.

Verification

• just gates < /dev/null passed, including browser realms, consumer smokes, packaged npm tests, and scheduler seeds.
• Wasmtime FIFO and seed 1: 614 passes, 62 known failures, 174 excluded commands, zero unexpected failures (previously 607 passes / 69 known failures).
• Official conformance: 1,468 passes, 38 expected failures, five unsupported directives; unchanged.
• Regression coverage rejects wrong-phase native/translation failures and distinguishes discriminant 2 of 2 cases from 3 of 3 cases.
• Consumer checkout statuses unchanged; independent review passed.

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