fix(ttfd): error when calling reportFullyDisplayed() twice

[buenaflor]

📜 Description

When completer is already finished then calling complete() on it again throws a StateError

💡 Motivation and Context

Fixes issue taken from SDK Crash Detection:

StateError: null
  #0      _AsyncCompleter.complete (dart:async/future_impl.dart:84)
  #1      TimeToFullDisplayTracker.reportFullyDisplayed (package:sentry_flutter/src/navigation/time_to_full_display_tracker.dart:80)
  #2      TimeToDisplayTracker.reportFullyDisplayed (package:sentry_flutter/src/navigation/time_to_display_tracker.dart:39)
  #3      SentryFlutter.reportFullyDisplayed (package:sentry_flutter/src/sentry_flutter.dart:245)
  #4      new Future.delayed.<fn> (dart:async/future.dart:417)
  #5      Timer._createTimer.<fn> (dart:async-patch/timer_patch.dart:18)
  #6      _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398)
  #7      _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429)
  #8      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184)

💚 How did you test it?

Unit test

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.81%. Comparing base (77b8ba7) to head (cc3a460).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
flutter/lib/src/sentry_flutter.dart	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2339      +/-   ##
==========================================
+ Coverage   86.38%   90.81%   +4.43%     
==========================================
  Files         247       73     -174     
  Lines        8615     2396    -6219     
==========================================
- Hits         7442     2176    -5266     
+ Misses       1173      220     -953     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[github-actions]

Android Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	487.74 ms	563.45 ms	75.70 ms
Size	6.49 MiB	7.56 MiB	1.07 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
8ced2dc	295.58 ms	336.49 ms	40.91 ms
559d28f	302.35 ms	339.53 ms	37.18 ms
62ae1b3	419.60 ms	494.14 ms	74.54 ms
6d7a391	331.94 ms	367.04 ms	35.10 ms
3ad66e4	406.90 ms	481.48 ms	74.58 ms
3334ac1	303.98 ms	366.65 ms	62.67 ms
0118295	365.71 ms	438.56 ms	72.85 ms
7e7f0b1	387.44 ms	459.14 ms	71.70 ms
fe4aa56	356.06 ms	428.67 ms	72.61 ms
25161f4	353.98 ms	431.94 ms	77.96 ms

App size

Revision	Plain	With Sentry	Diff
8ced2dc	6.06 MiB	7.03 MiB	990.29 KiB
559d28f	5.94 MiB	6.92 MiB	1001.70 KiB
62ae1b3	6.35 MiB	7.40 MiB	1.05 MiB
6d7a391	5.94 MiB	6.95 MiB	1.01 MiB
3ad66e4	6.33 MiB	7.26 MiB	947.04 KiB
3334ac1	6.06 MiB	7.03 MiB	993.54 KiB
0118295	6.33 MiB	7.26 MiB	947.07 KiB
7e7f0b1	6.35 MiB	7.34 MiB	1008.33 KiB
fe4aa56	6.06 MiB	7.10 MiB	1.04 MiB
25161f4	6.27 MiB	7.20 MiB	960.44 KiB

Previous results on branch: fix/ttfd-completer

Startup times

Revision	Plain	With Sentry	Diff
2e7d7ff	487.13 ms	535.53 ms	48.41 ms

App size

Revision	Plain	With Sentry	Diff
2e7d7ff	6.49 MiB	7.56 MiB	1.07 MiB

[github-actions]

iOS Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1255.50 ms	1278.49 ms	22.99 ms
Size	8.38 MiB	9.74 MiB	1.36 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
24b6e60	1250.69 ms	1268.63 ms	17.94 ms
2e1e4ae	1254.41 ms	1278.55 ms	24.14 ms
6a5a65d	1237.22 ms	1250.29 ms	13.07 ms
73d70bf	1249.08 ms	1268.41 ms	19.33 ms
7faee57	1232.65 ms	1246.10 ms	13.45 ms
43760f9	1216.07 ms	1238.51 ms	22.44 ms
6daa837	1250.42 ms	1265.60 ms	15.18 ms
d4120ac	1260.61 ms	1274.09 ms	13.47 ms
d883d62	1221.39 ms	1230.18 ms	8.80 ms
43abc4f	1248.33 ms	1272.86 ms	24.52 ms

App size

Revision	Plain	With Sentry	Diff
24b6e60	8.32 MiB	9.38 MiB	1.06 MiB
2e1e4ae	8.34 MiB	9.65 MiB	1.31 MiB
6a5a65d	8.34 MiB	9.65 MiB	1.31 MiB
73d70bf	8.38 MiB	9.70 MiB	1.33 MiB
7faee57	8.33 MiB	9.64 MiB	1.31 MiB
43760f9	8.29 MiB	9.36 MiB	1.07 MiB
6daa837	8.33 MiB	9.40 MiB	1.07 MiB
d4120ac	8.28 MiB	9.34 MiB	1.06 MiB
d883d62	8.29 MiB	9.36 MiB	1.07 MiB
43abc4f	8.33 MiB	9.54 MiB	1.21 MiB

Previous results on branch: fix/ttfd-completer

Startup times

Revision	Plain	With Sentry	Diff
2e7d7ff	1242.24 ms	1259.85 ms	17.61 ms

App size

Revision	Plain	With Sentry	Diff
2e7d7ff	8.38 MiB	9.74 MiB	1.36 MiB