Fix intermittent failures in fdc3.destructuredMethods conformance tests

[Roaders]

Mock apps opened via the destructured open() method could have their close listener registered after the test had already completed, and the cleanup step only allowed a 1 second window to receive the close confirmation. Wait for mock app initialization before proceeding, await the close broadcast, and use the existing mock-processing timeout instead of the hardcoded 1 second window.

Fixes #2114

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Review Checklist

• Issue: If a change was made to the FDC3 Standard, was an issue linked above?
• CHANGELOG: Is a CHANGELOG.md entry included?
• API changes: Does this PR include changes to any of the FDC3 APIs (DesktopAgent, Channel, PrivateChannel, Listener, Bridging)?
  • Docs & Sources: If yes, were both documentation (/docs) and sources updated?
    
    JSDoc comments on interfaces and types should be matched to the main documentation in /docs
  • Conformance tests: If yes, are conformance test definitions (/toolbox/fdc3-conformance) still correct and complete?
    
    Conformance test definitions should cover all required aspects of an FDC3 Desktop Agent implementation, which are usually marked with a MUST keyword, and optional features (SHOULD or MAY) where the format of those features is defined
  • Schemas: If yes, were changes applied to the Bridging and FDC3 for Web protocol schemas?
    
    The Web Connection protocol and Desktop Agent Communication Protocol schemas must be able to support all necessary aspects of the Desktop Agent API, while Bridging must support those aspects necessary for Desktop Agents to communicate with each other
    • If yes, was code generation (npm run build) run and the results checked in?
      
      Generated code will be found at /src/api/BrowserTypes.ts and/or /src/bridging/BridgingTypes.ts
• Context types: Were new Context type schemas created or modified in this PR?
  • Were the field type conventions adhered to?
  • Was the BaseContext schema applied via allOf (as it is in existing types)?
  • Was a title and description provided for all properties defined in the schema?
  • Was at least one example provided?
  • Was code generation (npm run build) run and the results checked in?
    
    Generated code will be found at /src/context/ContextTypes.ts
• Intents: Were new Intents created in this PR?
  • Were the intent name prefixes and other naming conventions & characteristics adhered to?
  • Was the new intent added to the list in the Intents Overview?

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.11%. Comparing base (715943c) to head (b37fdfc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2143   +/-   ##
=======================================
  Coverage   95.11%   95.11%           
=======================================
  Files          73       73           
  Lines        4196     4196           
  Branches      584      589    +5     
=======================================
  Hits         3991     3991           
  Misses        205      205           

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[julianna-ciq]

lgtm

[Roaders]

agreement to merge given in SWG #2153