fix(instrumentation-mysql, instrumentation-mongodb)!: replace deprecated db.client.connections.usage with db.client.connection.count in mongodb and mysql

[Luffy-nani]

Which problem is this PR solving?

-db.client.connections.usage is deprecated in favor of db.client.connection.count. The MongoDB and MySQL instrumentations still emit only the deprecated metric, with no path to the replacement.

Fixes #3590

Short description of the changes

• Replaced db.client.connections.usage with db.client.connection.count in both instrumentation-mongodb and instrumentation-mysql, emitted unconditionally — matching the pattern already used by instrumentation-pg (as confirmed in the discussion on feat!: only emit stable http, network and database attributes #3585).
• Updated existing tests in both packages to assert the new metric name (no new test files added).
• Updated both READMEs to document the new metric.

Related: #3585 (dependency, now merged)

[maryliag]

Added a few comments, mostly because you update the metric name, but not the attributes

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Status last refreshed: 2026-07-22 20:10:32 UTC.

• Status: Merged.

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This package does not have an assigned component owner and is considered unmaintained. As such this package is in feature-freeze and this PR will be closed with 14 days unless a new owner or a sponsor (a member of @open-telemetry/javascript-approvers) for the feature is found. It is the responsibility of the author to find a sponsor for this feature.
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[Luffy-nani]

Hey @maryliag , pushed a fix for all the comments: both packages now import and use db.client.connection.pool.name and db.client.connection.state from semconv instead of raw strings, and renamed poolNameOld to poolName in mysql. Let me know if I missed anything!
One thing I noticed while in there is getPoolNameOld() in mysql's utils.ts has the same "old" naming leftover. Didn't touch it since you didn't flag it, but happy to rename that too if you'd like.

[Luffy-nani]

Hi @maryliag ! Just a friendly follow-up on this PR 😊
I know you're probably busy, so no rush at all. Whenever you get a chance, I'd really appreciate another review. Thanks!

[maryliag]

just a few nits (make sure you import the constant accordingly)

[pichlermarc]

Looks like we need to merge this before releasing the semconv updates (ref #3596).
I'll address the nits to unblock this PR.

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