test(browser-plugin-media): cover updateMediaTracking mid-session empty-string stripping [AISP-1625]

[snowplow-claude-review]

What

Adds a Jest test for the updateMediaTracking mid-session path in the media plugin.

buildMediaPlayerEntity in plugins/browser-plugin-media/src/core.ts already deletes label, playerType, and quality when they equal '' before the entity is emitted. The existing tests in test/api.test.ts verified this only at startMediaTracking time. This PR adds the missing case: a session started with a non-empty label, followed by updateMediaTracking({ label: '' }) and trackMediaPlay, asserts that label is absent from the media player context entity on the subsequent event.

Why it matters

The updateMediaTracking path merges the supplied options into player state and then routes through buildMediaPlayerEntity on every subsequent track call (api.ts:109-114). Without this test, a regression in the state-merge path could reintroduce the empty-string emission without any test failure.

What to review

• plugins/browser-plugin-media/test/api.test.ts: the new test block — check that the assertion (label key absent from the entity properties) correctly targets the right context entity and property name.

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Draft PR opened for review — please verify and run CI before merging.

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