feat(V9): Make span read only in v9

[noahsmartin]

I suggest we make this readonly in V9. I don't think we want anyone setting it to any new types that conform to the protocol. Also, I want to remove SentrySerializable from the public API but this property needs to have the serialize function defined. If we want to allow it to be set publicly we will need to keep this function public to make sure anything that it gets set to has a serialize function. However, I think we can just make it readonly like this, allowing us to move the serialize aspect to a private header.

#skip-changelog

[github-actions]

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Generated by 🚫 dangerJS against 15cf346

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.678%. Comparing base (67e8e3e) to head (15cf346).
⚠️ Report is 5 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #5866       +/-   ##
=============================================
+ Coverage   86.667%   86.678%   +0.010%     
=============================================
  Files          423       423               
  Lines        36587     36587               
  Branches     17334     17330        -4     
=============================================
+ Hits         31709     31713        +4     
+ Misses        4831      4827        -4     
  Partials        47        47               

see 4 files with indirect coverage changes

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1214.27 ms	1240.30 ms	26.03 ms
Size	23.75 KiB	919.90 KiB	896.16 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
8da82b4	1220.08 ms	1248.24 ms	28.16 ms
ca91f42	1223.69 ms	1249.14 ms	25.45 ms
ea5a59b	1222.87 ms	1253.47 ms	30.60 ms
f97a070	1218.88 ms	1253.12 ms	34.24 ms
2bddb03	1214.11 ms	1246.78 ms	32.67 ms
76f74df	1238.29 ms	1261.22 ms	22.94 ms
fdea6f5	1216.08 ms	1241.82 ms	25.73 ms
d38165b	1211.41 ms	1242.49 ms	31.08 ms
7416ffc	1225.55 ms	1241.80 ms	16.25 ms
7f2f69c	1237.61 ms	1266.96 ms	29.35 ms

App size

Revision	Plain	With Sentry	Diff
8da82b4	23.75 KiB	913.63 KiB	889.88 KiB
ca91f42	23.75 KiB	913.63 KiB	889.88 KiB
ea5a59b	23.75 KiB	874.46 KiB	850.71 KiB
f97a070	23.75 KiB	858.68 KiB	834.93 KiB
2bddb03	23.75 KiB	891.01 KiB	867.26 KiB
76f74df	23.75 KiB	879.61 KiB	855.86 KiB
fdea6f5	23.75 KiB	867.15 KiB	843.40 KiB
d38165b	23.75 KiB	855.37 KiB	831.62 KiB
7416ffc	23.75 KiB	913.63 KiB	889.88 KiB
7f2f69c	23.75 KiB	913.38 KiB	889.63 KiB

Previous results on branch: spanReadonlyV9

Startup times

Revision	Plain	With Sentry	Diff
5ff3867	1233.48 ms	1254.88 ms	21.40 ms

App size

Revision	Plain	With Sentry	Diff
5ff3867	23.75 KiB	913.64 KiB	889.89 KiB

[philipphofmann]

Yep, let's do this. If users want to set the global span on the scope they should use the flag when starting a transaction. If users have some use cases for this, we can always add it back.