[Test]: improve reliability and correctness of serve-definitions tests

While reviewing serve-definition.test.ts, several test-quality issues were found that can lead to false positives, brittle tests, and reduced maintainability.
These are not breaking bugs but should be addressed to improve test correctness.

1:-Manual metricCalls increment bypasses real behavior

Here, metricCalls is incremented inside the test itself, not via the mocked metricURL request handled in ` mf.mock`.

1:-Shared mutable state across tests

This variable is shared across multiple ` Deno.test `blocks and reused in different contexts.
This creates:-
Implicit coupling between tests and Dependence on execution order or correct manual resets which reduces the tests Isolation.

3:-Unused test data (mockParam)

Here,` mockParam` is never used which increases noise and makes the test harder to reason about.

I am interested in solving this.

Read serve-definition.test.ts, focusing on the Deno.test blocks, metricCalls, mf.mock, and the unused mockParam shown in the issue. Run the serve-definitions tests first; done means the tests rely on the mocked metric request, avoid shared mutable state and manual resets, remove unused data, and retain reliable assertions.

Written by the indexing model from the issue text.