fix(core): Fix error handling when sending envelopes

[mydea]

I noticed that we actually handled errors in sendEnvelope incorrectly - we would resolve this function with the rejection reason, if sending fails. this does not match the type of TransportMakeRequestResponse, you could actually get something like this out (and the tests actually incorrectly tested this):

// transport.send() rejects with "fetch does not exist"
const res = await client.sendEnvelope(envelope);
// res --> "fetch does not exist" (string)

This PR fixes this to instead resolve with an empty object (which matches the expected return type).

Extracted this out of #17641 because it is actually a bug/fix.

[github-actions]

size-limit report 📦

⚠️ Warning: Base artifact is not the latest one, because the latest workflow run is not done yet. This may lead to incorrect results. Try to re-run all tests to get up to date results.

Path	Size	% Change	Change
@sentry/browser	24.16 kB	-0.05%	-12 B 🔽
@sentry/browser - with treeshaking flags	22.72 kB	-0.03%	-5 B 🔽
@sentry/browser (incl. Tracing)	40.16 kB	-0.03%	-10 B 🔽
@sentry/browser (incl. Tracing, Replay)	78.53 kB	-0.02%	-10 B 🔽
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	68.24 kB	-0.01%	-4 B 🔽
@sentry/browser (incl. Tracing, Replay with Canvas)	83.19 kB	-0.02%	-12 B 🔽
@sentry/browser (incl. Tracing, Replay, Feedback)	95.4 kB	-0.02%	-11 B 🔽
@sentry/browser (incl. Feedback)	40.87 kB	-0.03%	-11 B 🔽
@sentry/browser (incl. sendFeedback)	28.81 kB	-0.04%	-10 B 🔽
@sentry/browser (incl. FeedbackAsync)	33.75 kB	-0.03%	-9 B 🔽
@sentry/react	25.88 kB	-0.02%	-5 B 🔽
@sentry/react (incl. Tracing)	42.16 kB	-0.01%	-4 B 🔽
@sentry/vue	28.64 kB	-0.04%	-11 B 🔽
@sentry/vue (incl. Tracing)	41.98 kB	-0.03%	-11 B 🔽
@sentry/svelte	24.19 kB	-0.05%	-11 B 🔽
CDN Bundle	25.74 kB	-0.04%	-8 B 🔽
CDN Bundle (incl. Tracing)	40.05 kB	-0.02%	-8 B 🔽
CDN Bundle (incl. Tracing, Replay)	76.27 kB	-0.02%	-8 B 🔽
CDN Bundle (incl. Tracing, Replay, Feedback)	81.78 kB	-0.01%	-6 B 🔽
CDN Bundle - uncompressed	75.18 kB	-0.02%	-15 B 🔽
CDN Bundle (incl. Tracing) - uncompressed	118.5 kB	-0.02%	-15 B 🔽
CDN Bundle (incl. Tracing, Replay) - uncompressed	233.6 kB	-0.01%	-16 B 🔽
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	246.37 kB	-0.01%	-16 B 🔽
@sentry/nextjs (client)	44.15 kB	-0.02%	-5 B 🔽
@sentry/sveltekit (client)	40.6 kB	-0.02%	-7 B 🔽
@sentry/node-core	49.86 kB	-0.02%	-6 B 🔽
@sentry/node	151.14 kB	-0.01%	-7 B 🔽
@sentry/node - without tracing	91.75 kB	-0.01%	-3 B 🔽
@sentry/aws-serverless	105.19 kB	-0.01%	-4 B 🔽

View base workflow run

[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.
⚠️ Warning: Base artifact is not the latest one, because the latest workflow run is not done yet. This may lead to incorrect results. Try to re-run all tests to get up to date results.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,191	-	8,898	+3%
GET With Sentry	1,400	15%	1,334	+5%
GET With Sentry (error only)	6,082	66%	5,980	+2%
POST Baseline	1,211	-	1,189	+2%
POST With Sentry	522	43%	510	+2%
POST With Sentry (error only)	1,067	88%	1,041	+2%
MYSQL Baseline	3,316	-	3,277	+1%
MYSQL With Sentry	487	15%	484	+1%
MYSQL With Sentry (error only)	2,721	82%	2,627	+4%

View base workflow run