ref(core): Make spanStreamingIntegration tree-shakeable via __SENTRY_TRACING__ flag

[Lms24]

Guards the automatic spanStreamingIntegration push behind __SENTRY_TRACING__ so that bundlers configured to tree-shake tracing can actually drop the integration. This should remove ~2KB of gzipped dead code for anyone who doesn't care about tracing.

[github-actions]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	29.86 kB	+0.08%	+21 B 🔺
@sentry/browser - with treeshaking flags	28.05 kB	+0.08%	+22 B 🔺
@sentry/browser (incl. Tracing)	47.27 kB	+0.06%	+24 B 🔺
@sentry/browser (incl. Tracing + Span Streaming)	47.3 kB	+0.06%	+27 B 🔺
@sentry/browser (incl. Tracing, Profiling)	52.03 kB	+0.06%	+29 B 🔺
@sentry/browser (incl. Tracing, Replay)	86.61 kB	+0.02%	+17 B 🔺
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	76.04 kB	+0.04%	+30 B 🔺
@sentry/browser (incl. Tracing, Replay with Canvas)	91.31 kB	+0.04%	+31 B 🔺
@sentry/browser (incl. Tracing, Replay, Feedback)	103.99 kB	+0.04%	+37 B 🔺
@sentry/browser (incl. Feedback)	47.17 kB	+0.08%	+36 B 🔺
@sentry/browser (incl. sendFeedback)	34.69 kB	+0.07%	+22 B 🔺
@sentry/browser (incl. FeedbackAsync)	39.8 kB	+0.06%	+23 B 🔺
@sentry/browser (incl. Metrics)	30.93 kB	+0.07%	+21 B 🔺
@sentry/browser (incl. Logs)	31.17 kB	+0.08%	+22 B 🔺
@sentry/browser (incl. Metrics & Logs)	31.84 kB	+0.07%	+21 B 🔺
@sentry/react	31.65 kB	+0.07%	+22 B 🔺
@sentry/react (incl. Tracing)	49.53 kB	+0.05%	+21 B 🔺
@sentry/vue	34.95 kB	+0.07%	+23 B 🔺
@sentry/vue (incl. Tracing)	49.27 kB	+0.07%	+33 B 🔺
@sentry/svelte	29.88 kB	+0.08%	+23 B 🔺
CDN Bundle	31.89 kB	+0.08%	+23 B 🔺
CDN Bundle (incl. Tracing)	47.56 kB	+0.05%	+23 B 🔺
CDN Bundle (incl. Logs, Metrics)	33.43 kB	+0.06%	+19 B 🔺
CDN Bundle (incl. Tracing, Logs, Metrics)	48.97 kB	+0.06%	+25 B 🔺
CDN Bundle (incl. Replay, Logs, Metrics)	72.77 kB	+0.03%	+20 B 🔺
CDN Bundle (incl. Tracing, Replay)	85.21 kB	+0.03%	+22 B 🔺
CDN Bundle (incl. Tracing, Replay, Logs, Metrics)	86.52 kB	+0.03%	+24 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback)	91.03 kB	+0.03%	+20 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics)	92.33 kB	+0.03%	+21 B 🔺
CDN Bundle - uncompressed	94.68 kB	+0.07%	+61 B 🔺
CDN Bundle (incl. Tracing) - uncompressed	142.18 kB	+0.05%	+61 B 🔺
CDN Bundle (incl. Logs, Metrics) - uncompressed	99.3 kB	+0.07%	+61 B 🔺
CDN Bundle (incl. Tracing, Logs, Metrics) - uncompressed	146.16 kB	+0.05%	+61 B 🔺
CDN Bundle (incl. Replay, Logs, Metrics) - uncompressed	224 kB	+0.03%	+61 B 🔺
CDN Bundle (incl. Tracing, Replay) - uncompressed	261.44 kB	+0.03%	+61 B 🔺
CDN Bundle (incl. Tracing, Replay, Logs, Metrics) - uncompressed	265.4 kB	+0.03%	+61 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	275.14 kB	+0.03%	+61 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics) - uncompressed	279.1 kB	+0.03%	+61 B 🔺
@sentry/nextjs (client)	52.1 kB	+0.05%	+21 B 🔺
@sentry/sveltekit (client)	47.73 kB	+0.05%	+23 B 🔺
@sentry/core/server	65.55 kB	+0.04%	+23 B 🔺
@sentry/core/browser	51.88 kB	-	-
@sentry/node	120.26 kB	+0.03%	+25 B 🔺
@sentry/node/import (ESM hook with diagnostics-channel injection)	0 B	added	added
@sentry/node - without tracing	82.94 kB	-0.91%	-754 B 🔽
@sentry/aws-serverless	92.37 kB	+0.03%	+19 B 🔺
@sentry/cloudflare (withSentry) - minified	218.7 kB	+0.03%	+53 B 🔺
@sentry/cloudflare (withSentry)	538.92 kB	+0.02%	+69 B 🔺
@sentry/browser - with treeshaking flags tracing without tracing	26.37 kB	added	added

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[logaretm]

Browser CDN bundle size didn't go down, is something off there?

[Lms24]

the browser CDN bundle never set the flag because even for errors-only, users can still use Sentry.startSpan. errors-only, only doesn't include the tracing integrations.

This is purely used for shaking out tracing integrations if users don't want any tracing, hence the warning in docs.

SENTRY_TRACING must not be replaced with false when you're using any tracing-related SDK features (for example, Sentry.startSpan()).

I realized this flag isn't used a lot and either could/should be used more, or we should repurpose it. Problem is that every guard increases bundle size for default users 🙃