Fix a data race for SentryId.empty

[philipphofmann]

📜 Description

Initialize the SentryId.empty in the class initializer to fix a data race.

💡 Motivation and Context

Came up in #3069.

💚 How did you test it?

Unit tests.

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1199.39 ms	1212.00 ms	12.61 ms
Size	20.76 KiB	435.35 KiB	414.59 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d3abae0	1200.36 ms	1224.22 ms	23.87 ms
b9b0f0a	1239.76 ms	1257.68 ms	17.92 ms
154f795	1250.38 ms	1274.54 ms	24.16 ms
56ec5d0	1236.65 ms	1261.90 ms	25.25 ms
98a8c16	1206.40 ms	1232.14 ms	25.74 ms
25a5e8b	1235.16 ms	1255.47 ms	20.30 ms
b1b7d72	1246.31 ms	1261.00 ms	14.69 ms
e1eed6b	1259.08 ms	1270.57 ms	11.49 ms
25bcc50	1240.47 ms	1254.70 ms	14.23 ms
302ee8b	1194.02 ms	1223.34 ms	29.32 ms

App size

Revision	Plain	With Sentry	Diff
d3abae0	20.76 KiB	434.92 KiB	414.16 KiB
b9b0f0a	20.76 KiB	434.94 KiB	414.18 KiB
154f795	20.76 KiB	435.25 KiB	414.49 KiB
56ec5d0	20.76 KiB	414.44 KiB	393.69 KiB
98a8c16	20.76 KiB	431.00 KiB	410.24 KiB
25a5e8b	20.76 KiB	436.33 KiB	415.57 KiB
b1b7d72	20.76 KiB	436.33 KiB	415.57 KiB
e1eed6b	20.76 KiB	432.17 KiB	411.41 KiB
25bcc50	20.76 KiB	427.22 KiB	406.46 KiB
302ee8b	20.76 KiB	419.62 KiB	398.87 KiB

Previous results on branch: fix/sentry-id-empty-data-race

Startup times

Revision	Plain	With Sentry	Diff
0c99bb6	1204.65 ms	1233.14 ms	28.49 ms

App size

Revision	Plain	With Sentry	Diff
0c99bb6	20.76 KiB	434.98 KiB	414.22 KiB

[codecov]

Codecov Report

Merging #3072 (b6e189a) into main (154f795) will decrease coverage by 0.060%.
The diff coverage is 100.000%.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3072       +/-   ##
=============================================
- Coverage   88.840%   88.780%   -0.060%     
=============================================
  Files          493       493               
  Lines        53164     53148       -16     
  Branches     19049     19042        -7     
=============================================
- Hits         47231     47185       -46     
- Misses        4971      4996       +25     
- Partials       962       967        +5     

Impacted Files	Coverage Δ
Sources/Sentry/SentryId.m	100.000% <100.000%> (ø)
Tests/SentryTests/Protocol/SentryIdTests.swift	100.000% <100.000%> (ø)

... and 12 files with indirect coverage changes

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