Add test coverage for FuncHostDebugViewProvider

[Copilot]

Adds missing test coverage for the Function Host Debug View components introduced in #4883.

Test coverage:

• Tree item creation for all node types (noHost, hostTask, hostError)
• Type guard validation (isHostTaskNode, isHostErrorNode) with edge cases
• Refresh event emission
• getChildren behavior for different node types

Exports for testing:

• FuncHostDebugViewProvider class
• Type guard functions (isHostTaskNode, isHostErrorNode)

Tests follow existing repository patterns using Mocha.

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[Copilot]

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