ottl: improve Len() unsupported type error diagnostics

[rite7sh]

Description

Enhances error diagnostics in the Len() OTTL function by including the runtime type when an unsupported target type is encountered.

Previously, unsupported types returned a generic error message:

errors.New(typeError)

This change replaces it with:

fmt.Errorf("Len: unsupported target type %T. %s", val, typeError)

This improves debugging clarity for OTTL users without modifying execution logic, control flow, or return values for valid inputs.

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Link to tracking issue

N/A — small diagnostic improvement aligned with ongoing OTTL type‑system stabilization and compilation optimization efforts.

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Testing

• Ran targeted tests for Len():
  go test -v -run Len ./pkg/ottl/ottlfuncs
• Executed full ottlfuncs package tests
• Executed full OTTL module tests
• Verified error paths still trigger correctly
• Confirmed success paths remain unchanged
• No test assertions depended on exact error string text

All tests pass successfully.

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Documentation

No documentation changes required.

This change only improves runtime error diagnostics and does not alter user‑facing configuration or function behavior.

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[paulojmdias]

/workflow-approve

[paulojmdias]

/workflow-approve

[paulojmdias]

/workflow-approve

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