feat(ecs): merge imports plugins at runtime (types still exclude them)

[krisnye]

Summary

Follow-up to #118. imports was previously type-only — the imported plugins' members were visible to local declarations but contributed nothing at runtime. That meant a consumer who forgot to re-list an imported plugin in the top-level combine(...) got undefined transactions/resources at runtime despite a clean compile.

This makes imports merge into the assembled plugin at runtime exactly like extends (order: imports → extends → local declarations, preserving service initialization order).

This is a pure runtime change — no type changes

The result type is unchanged and still excludes the imported members. That's the whole point: it preserves the property that kills the quadratic extends blowup (imported members do not propagate through downstream result types). The public function signature is identical; only the function body changed.

So:

	result type	runtime plugin
extends	includes base	includes base
imports (before)	excludes	excluded ← footgun
imports (now)	excludes	includes ✓

Verification

• tsc -b green; 62 plugin tests pass (added an "imports runtime behavior" suite proving imported members exist on the assembled plugin and on a database built from it alone, with no separate combine); lint clean.
• The existing imports-chain.type-test.ts still passes unchanged — imported members remain absent from the result type.
• Also fixes doc comments that incorrectly told consumers they must re-list imports, and removes a stray artifact in the typeperf README.

Bump to 0.9.65.

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