chore: Some decodable updates for V9

[noahsmartin]

Splitting this out as a separate change from #6348 to make the PRs smaller

#skip-changelog

Closes #6358

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.813%. Comparing base (7aaa0b6) to head (5abd735).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #6357       +/-   ##
=============================================
- Coverage   86.818%   86.813%   -0.006%     
=============================================
  Files          438       438               
  Lines        37311     37311               
  Branches     17428     17427        -1     
=============================================
- Hits         32393     32391        -2     
+ Misses        4874      4644      -230     
- Partials        44       276      +232     

Files with missing lines	Coverage Δ
Sources/Sentry/SentryUser.m	96.407% <100.000%> (ø)
...ces/Swift/Protocol/Codable/SentryUserCodable.swift	100.000% <ø> (ø)

... and 38 files with indirect coverage changes

---

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1232.25 ms	1264.56 ms	32.31 ms
Size	23.75 KiB	990.00 KiB	966.26 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
2ec2700	1238.28 ms	1258.82 ms	20.53 ms
d0f70ce	1226.54 ms	1247.04 ms	20.50 ms
5bf2b17	1213.53 ms	1238.54 ms	25.01 ms
efab7d3	1219.98 ms	1252.12 ms	32.14 ms
e3ebff3	1223.47 ms	1249.27 ms	25.80 ms
7b3399c	1193.35 ms	1227.38 ms	34.03 ms
3133d0e	1237.86 ms	1262.87 ms	25.01 ms
22b6996	1234.00 ms	1263.24 ms	29.24 ms
43597ba	1214.88 ms	1243.52 ms	28.65 ms
fc6557e	1226.40 ms	1249.88 ms	23.48 ms

App size

Revision	Plain	With Sentry	Diff
2ec2700	23.75 KiB	980.80 KiB	957.05 KiB
d0f70ce	23.75 KiB	913.09 KiB	889.34 KiB
5bf2b17	23.75 KiB	913.27 KiB	889.52 KiB
efab7d3	23.75 KiB	912.78 KiB	889.03 KiB
e3ebff3	23.75 KiB	878.48 KiB	854.73 KiB
7b3399c	23.75 KiB	946.68 KiB	922.94 KiB
3133d0e	23.74 KiB	976.79 KiB	953.04 KiB
22b6996	23.75 KiB	908.02 KiB	884.27 KiB
43597ba	23.75 KiB	880.32 KiB	856.58 KiB
fc6557e	23.75 KiB	866.68 KiB	842.93 KiB

[philipphofmann]

LGTM