ref(tests): Add TestEnv class to Node integration tests.

[onurtemizkan]

Following up: #5579 and #5596
Ref: #5579 (review)

Refactored Node integration test helpers, to use a TestEnv instance for each test. This will help avoid explicitly passing server and url back and forth.

Remix server-side tests also extend the TestEnv class to implement Remix-specific initialization logic.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.41 KB (+0.03% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	60.06 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	17.98 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	52.92 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	19.77 KB (0%)
@sentry/browser - Webpack (minified)	64.31 KB (0%)
@sentry/react - Webpack (gzipped + minified)	19.79 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	44.7 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.9 KB (+0.01% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.27 KB (+0.01% 🔺)

[AbhiPrasad]

We'll need to rebase this on top of #5512 - otherwise looks great to me!

[onurtemizkan]

@AbhiPrasad - rebased the PR 👍