fix(profiling): various fixes needed for chunk envelopes to validate

[armcknight]

After pairing up with @phacops and @Zylphrex , we identified a few changes needed to get continuous profiling chunk envelopes accepted by the backend.

• we need to use standard unix epoch instead of apple's newer reference date
• need GPU value units to be correctly stated as nanoseconds (mistakenly changed it to "milliseconds" when changing the timestamps to a non-nanosecond-integer value)
• need the envelope header ID (which is also injected as the event ID) to be the same as the chunk ID

for #3555; #skip-changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.157%. Comparing base (d9280ee) to head (5a404e0).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4058       +/-   ##
=============================================
+ Coverage   91.129%   91.157%   +0.028%     
=============================================
  Files          610       611        +1     
  Lines        47988     48076       +88     
  Branches     17192     17264       +72     
=============================================
+ Hits         43731     43825       +94     
+ Misses        4164      4160        -4     
+ Partials        93        91        -2     

Files	Coverage Δ
...es/Sentry/Profiling/SentryProfilerSerialization.mm	91.153% <100.000%> (+0.034%)	⬆️
Sources/Sentry/Profiling/SentryProfilerState.mm	99.275% <100.000%> (ø)
Sources/Sentry/SentryFramesTracker.m	99.310% <100.000%> (-0.005%)	⬇️
Sources/Sentry/SentryMetricProfiler.mm	97.790% <100.000%> (ø)

... and 17 files with indirect coverage changes

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1217.85 ms	1229.71 ms	11.87 ms
Size	21.58 KiB	669.82 KiB	648.24 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
efb0147	1242.00 ms	1257.31 ms	15.31 ms
ecd9ecd	1191.76 ms	1216.92 ms	25.16 ms
4d68229	1233.50 ms	1262.92 ms	29.42 ms
608755c	1220.23 ms	1239.76 ms	19.52 ms
2719ce6	1211.75 ms	1237.16 ms	25.41 ms
24c8a0f	1224.65 ms	1232.69 ms	8.03 ms
e998fd0	1241.49 ms	1262.63 ms	21.14 ms
230ba67	1230.18 ms	1252.32 ms	22.13 ms
881a955	1254.14 ms	1268.43 ms	14.29 ms
d914696	1225.76 ms	1238.83 ms	13.08 ms

App size

Revision	Plain	With Sentry	Diff
efb0147	22.84 KiB	403.52 KiB	380.67 KiB
ecd9ecd	20.76 KiB	420.23 KiB	399.47 KiB
4d68229	20.76 KiB	432.34 KiB	411.58 KiB
608755c	20.76 KiB	436.33 KiB	415.57 KiB
2719ce6	20.76 KiB	435.13 KiB	414.37 KiB
24c8a0f	21.58 KiB	418.69 KiB	397.11 KiB
e998fd0	21.58 KiB	414.59 KiB	393.01 KiB
230ba67	20.76 KiB	427.35 KiB	406.59 KiB
881a955	22.85 KiB	407.63 KiB	384.79 KiB
d914696	21.58 KiB	629.83 KiB	608.25 KiB

[philipphofmann]

LGTM