🐛 Avoid duplicating inherited API middleware

[taras]

Motivation

When a child scope adds contextual API middleware after inheriting middleware from its parent, Effection 4.1 stores the inherited middleware as part of the child's local decoration. If the parent later adds more middleware, propagation recomputes the inherited total and applies the original parent middleware twice.

This blocks @effectionx/context-api from delegating to Effection's experimental createApi without regressing its existing live-parent middleware guarantees.

Approach

• Separate the inherited middleware total from child-local middleware when a scope first decorates an API.
• Keep later ancestor propagation live while ensuring each inherited middleware appears exactly once.
• Add a regression test covering parent middleware installed both before and after a child installs its own middleware.

Verification

• deno task test — 37 suites, 234 steps passed
• deno lint
• deno check mod.ts experimental.ts
• deno fmt lib/api-internal.ts test/api.test.ts
• deno task build:npm 4.1.1

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/effection@1226

commit: 626c8cf

[codspeed-hq]

Merging this PR will not alter performance

✅ 6 untouched benchmarks

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_{Comparing agent/fix-api-inheritance (626c8cf) with v4 (70ddc1c)}

[github-actions]

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