refactor: Add nullability property for screenName

[philprime]

This PR is derived from #5572 in an effort to make the large amount of changes easier to review for #5577.

Changes the parameter screenName to be nullable, as the method implementation allows it.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
31824	1	31823	97

View the top 1 failed test(s) by shortest run time

iOS_SwiftUI_UITests.LaunchUITests::testTTID_TTFD

Stack Traces | 0s run time

.../iOS-SwiftUI/iOS-SwiftUI-UITests/LaunchUITests.swift:81 - Failed to terminate io.sentry.iOS-SwiftUI:8923: Failed to terminate io.sentry.iOS-SwiftUI:0

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1244.96 ms	1267.14 ms	22.18 ms
Size	23.75 KiB	913.17 KiB	889.42 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
f92cfa9	1217.94 ms	1240.06 ms	22.12 ms
63ac649	1192.10 ms	1216.78 ms	24.68 ms
cda95fc	1231.42 ms	1247.18 ms	15.77 ms
80a5166	1224.49 ms	1251.29 ms	26.80 ms
b714cb9	1224.71 ms	1238.04 ms	13.33 ms
ac4739e	1236.55 ms	1258.89 ms	22.34 ms
2bddb03	1214.11 ms	1246.78 ms	32.67 ms
079bcc8	1217.88 ms	1234.88 ms	17.00 ms
7148f97	1235.09 ms	1258.07 ms	22.98 ms
9e0030e	1222.78 ms	1242.23 ms	19.45 ms

App size

Revision	Plain	With Sentry	Diff
f92cfa9	23.75 KiB	855.38 KiB	831.63 KiB
63ac649	23.75 KiB	855.38 KiB	831.63 KiB
cda95fc	23.75 KiB	912.77 KiB	889.02 KiB
80a5166	23.75 KiB	904.53 KiB	880.78 KiB
b714cb9	23.75 KiB	858.69 KiB	834.93 KiB
ac4739e	23.75 KiB	872.67 KiB	848.92 KiB
2bddb03	23.75 KiB	891.01 KiB	867.26 KiB
079bcc8	23.74 KiB	874.07 KiB	850.33 KiB
7148f97	23.75 KiB	854.78 KiB	831.03 KiB
9e0030e	23.75 KiB	893.72 KiB	869.97 KiB

[philipphofmann]

Thanks for keeping the PRs small.