enh: remove async from FlutterErrorIntegration

[buenaflor]

📜 Description

Removes unnecessary async usage, we don't need to await on captureEvent

💡 Motivation and Context

Fixes #3186

💚 How did you test it?

Existing tests

📝 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.84%. Comparing base (68e9ac1) to head (3ff853c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3202      +/-   ##
==========================================
+ Coverage   87.74%   89.84%   +2.10%     
==========================================
  Files         289       94     -195     
  Lines        9899     3389    -6510     
==========================================
- Hits         8686     3045    -5641     
+ Misses       1213      344     -869     

☔ View full report in Codecov by Sentry.
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[github-actions]

Android Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	478.92 ms	498.51 ms	19.59 ms
Size	13.93 MiB	14.93 MiB	1.00 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
93b7728	475.28 ms	489.13 ms	13.86 ms
c8596a6	474.00 ms	492.96 ms	18.96 ms
73a3c38	478.18 ms	526.62 ms	48.44 ms
0fb45d0	482.79 ms	554.02 ms	71.23 ms
640ad0c	466.00 ms	552.67 ms	86.67 ms
765aa8b	493.51 ms	531.23 ms	37.72 ms
cc4e375	426.15 ms	482.34 ms	56.19 ms
c1e775e	482.36 ms	608.98 ms	126.62 ms
2d34233	470.54 ms	558.90 ms	88.36 ms
54acf91	487.24 ms	529.60 ms	42.36 ms

App size

Revision	Plain	With Sentry	Diff
93b7728	6.54 MiB	7.69 MiB	1.15 MiB
c8596a6	6.54 MiB	7.53 MiB	1015.27 KiB
73a3c38	6.54 MiB	7.69 MiB	1.15 MiB
0fb45d0	6.54 MiB	7.70 MiB	1.17 MiB
640ad0c	6.54 MiB	7.69 MiB	1.15 MiB
765aa8b	6.54 MiB	7.70 MiB	1.16 MiB
cc4e375	6.54 MiB	7.69 MiB	1.15 MiB
c1e775e	6.54 MiB	7.70 MiB	1.17 MiB
2d34233	6.54 MiB	7.55 MiB	1.01 MiB
54acf91	6.54 MiB	7.70 MiB	1.17 MiB

[github-actions]

iOS Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1255.94 ms	1257.50 ms	1.56 ms
Size	5.53 MiB	5.96 MiB	443.81 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
827bf09	1261.86 ms	1276.41 ms	14.55 ms
73dca78	1246.65 ms	1265.42 ms	18.76 ms
6ba4675	1223.12 ms	1238.17 ms	15.04 ms
81f83eb	1259.53 ms	1273.39 ms	13.86 ms
0929dbf	1275.89 ms	1282.22 ms	6.33 ms
4481076	1256.48 ms	1266.64 ms	10.17 ms
dbd526b	1244.78 ms	1259.02 ms	14.24 ms
2cb90b9	1272.90 ms	1285.55 ms	12.66 ms
640ad0c	1241.04 ms	1253.96 ms	12.92 ms
4298701	1243.56 ms	1262.29 ms	18.72 ms

App size

Revision	Plain	With Sentry	Diff
827bf09	7.86 MiB	9.44 MiB	1.58 MiB
73dca78	7.86 MiB	9.44 MiB	1.58 MiB
6ba4675	7.86 MiB	9.44 MiB	1.58 MiB
81f83eb	7.86 MiB	9.44 MiB	1.58 MiB
0929dbf	7.86 MiB	9.54 MiB	1.69 MiB
4481076	7.86 MiB	9.44 MiB	1.58 MiB
dbd526b	7.86 MiB	9.44 MiB	1.58 MiB
2cb90b9	7.86 MiB	9.54 MiB	1.69 MiB
640ad0c	7.86 MiB	9.44 MiB	1.58 MiB
4298701	20.70 MiB	22.46 MiB	1.76 MiB