fix(core): Remove outdated _experiments.enableMetrics references from metrics JSDoc

[chargome]

Metrics are enabled by default and no longer require the _experiments.enableMetrics flag. This removes the outdated JSDoc @summary references in count(), gauge(), and distribution() that still mentioned needing to enable the experimental option.

Closes #19253 (added automatically)

[github-actions]

Codecov Results 📊

---

Generated by Codecov Action

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,886	-	8,882	+0%
GET With Sentry	1,778	20%	1,756	+1%
GET With Sentry (error only)	6,067	68%	6,178	-2%
POST Baseline	1,173	-	1,182	-1%
POST With Sentry	587	50%	592	-1%
POST With Sentry (error only)	1,038	88%	1,038	-
MYSQL Baseline	3,364	-	3,315	+1%
MYSQL With Sentry	463	14%	446	+4%
MYSQL With Sentry (error only)	2,718	81%	2,680	+1%

View base workflow run