feat(nuxt): implement server middleware instrumentation

[logaretm]

This pull request introduces instrumentation for Nuxt middleware, ensuring that all middleware handlers are automatically wrapped with tracing and error reporting functionality. The integration is achieved through build-time transformation.

recap:

• Adds a new build-time Rollup plugin (middlewareInstrumentationPlugin) that automatically wraps all detected middleware handlers with Sentry instrumentation during the Nitro build process.
• Implements the wrapMiddlewareHandler utility, which wraps middleware handlers to start a Sentry span, capture request data, record exceptions, and flush events in serverless environments.
• Updates the Nuxt module setup to inject Sentry middleware imports and instrumentation hooks during initialization, ensuring the new tracing logic is included in server builds.

TODO:

• Test traces and span visibility.
• Add unit/integration tests.
• Add E2E tests.
• Check to see if there are other ways to add middleware that would bypass the transformer.

[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	8,588	-	8,926	-4%
GET With Sentry	1,338	16%	1,388	-4%
GET With Sentry (error only)	6,109	71%	6,167	-1%
POST Baseline	1,197	-	1,192	+0%
POST With Sentry	528	44%	521	+1%
POST With Sentry (error only)	1,063	89%	1,034	+3%
MYSQL Baseline	3,338	-	3,366	-1%
MYSQL With Sentry	513	15%	468	+10%
MYSQL With Sentry (error only)	2,754	83%	2,732	+1%

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