Add sent_at to envelope header

[denrase]

📜 Description

• Add sent_at to envelope header
• Add in HttpTransport

💡 Motivation and Context

Closes #1337

💚 How did you test it?

• Unit test

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against 212ade7

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (c3b5126) 90.53% compared to head (212ade7) 90.53%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1428      +/-   ##
==========================================
- Coverage   90.53%   90.53%   -0.01%     
==========================================
  Files         175      175              
  Lines        5503     5502       -1     
==========================================
- Hits         4982     4981       -1     
  Misses        521      521              

Impacted Files	Coverage Δ
dart/lib/src/sentry_envelope_header.dart	100.00% <100.00%> (ø)
dart/lib/src/transport/http_transport.dart	93.93% <100.00%> (-0.27%)	⬇️

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[github-actions]

Android Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	309.06 ms	364.42 ms	55.36 ms
Size	6.15 MiB	7.11 MiB	981.82 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
ed605cc	317.48 ms	374.24 ms	56.76 ms
40680d3	323.55 ms	390.29 ms	66.73 ms
5112c69	333.67 ms	363.74 ms	30.08 ms
21d4150	379.31 ms	449.23 ms	69.93 ms
519423f	357.00 ms	415.77 ms	58.77 ms
d61cecf	339.69 ms	387.57 ms	47.88 ms
a49594a	282.27 ms	344.84 ms	62.57 ms
a094100	388.02 ms	459.50 ms	71.48 ms
0ceb89c	304.57 ms	357.18 ms	52.61 ms
c1bb00f	303.77 ms	371.88 ms	68.11 ms

App size

Revision	Plain	With Sentry	Diff
ed605cc	6.06 MiB	7.03 MiB	993.53 KiB
40680d3	6.06 MiB	7.03 MiB	989.25 KiB
5112c69	5.94 MiB	6.96 MiB	1.02 MiB
21d4150	5.94 MiB	6.97 MiB	1.03 MiB
519423f	6.06 MiB	7.03 MiB	989.24 KiB
d61cecf	6.06 MiB	7.03 MiB	995.56 KiB
a49594a	5.94 MiB	6.95 MiB	1.01 MiB
a094100	5.94 MiB	6.96 MiB	1.02 MiB
0ceb89c	5.94 MiB	6.95 MiB	1.01 MiB
c1bb00f	6.06 MiB	7.09 MiB	1.03 MiB

Previous results on branch: feat/sent-at-header

Startup times

Revision	Plain	With Sentry	Diff
8392f59	343.18 ms	403.96 ms	60.78 ms
a606145	326.16 ms	388.47 ms	62.31 ms

App size

Revision	Plain	With Sentry	Diff
8392f59	6.15 MiB	7.11 MiB	981.82 KiB
a606145	6.06 MiB	7.03 MiB	996.99 KiB

[github-actions]

iOS Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1243.39 ms	1259.10 ms	15.71 ms
Size	8.29 MiB	9.37 MiB	1.08 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6957bfd	1283.80 ms	1289.00 ms	5.20 ms
1131914	1277.20 ms	1300.20 ms	23.00 ms
ad69abc	1259.00 ms	1261.60 ms	2.60 ms
0be962b	1264.10 ms	1281.16 ms	17.06 ms
e66e71e	1273.55 ms	1291.63 ms	18.08 ms
3637a22	1290.39 ms	1318.42 ms	28.03 ms
9928a74	1249.98 ms	1269.08 ms	19.10 ms
b49bf00	1248.00 ms	1260.35 ms	12.35 ms
633cf2e	1257.96 ms	1275.73 ms	17.77 ms
e893df5	1247.90 ms	1262.31 ms	14.41 ms

App size

Revision	Plain	With Sentry	Diff
6957bfd	8.15 MiB	9.15 MiB	1020.71 KiB
1131914	8.16 MiB	9.17 MiB	1.01 MiB
ad69abc	8.10 MiB	9.08 MiB	1004.37 KiB
0be962b	8.10 MiB	9.16 MiB	1.07 MiB
e66e71e	8.10 MiB	9.08 MiB	1004.36 KiB
3637a22	8.09 MiB	9.07 MiB	1001.02 KiB
9928a74	8.16 MiB	9.17 MiB	1.01 MiB
b49bf00	8.10 MiB	9.08 MiB	1004.36 KiB
633cf2e	8.15 MiB	9.12 MiB	986.26 KiB
e893df5	8.09 MiB	9.07 MiB	1001.04 KiB

Previous results on branch: feat/sent-at-header

Startup times

Revision	Plain	With Sentry	Diff
8392f59	1245.32 ms	1247.43 ms	2.11 ms
a606145	1239.27 ms	1259.88 ms	20.61 ms

App size

Revision	Plain	With Sentry	Diff
8392f59	8.29 MiB	9.37 MiB	1.08 MiB
a606145	8.10 MiB	9.18 MiB	1.08 MiB

[marandaneto]

Thanks @denrase