test(core): add coverage for normalizeUrl error path

[saurabhsharma2u]

This PR adds a new test case normalizeUrl: invalid URL to plugins/core/tests/normalize.test.ts.
It verifies that normalizeUrl returns null for:

• Relative URLs without a base
• Invalid URL strings
• Invalid base URLs

This improves test coverage by exercising the catch block in normalizeUrl which handles new URL() exceptions.

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PR created automatically by Jules for task 5542858060731681841 started by @saurabhsharma2u

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