fix: Replace aiofile with aiofiles to prevent caio context leak under concurrent execution

[erichare]

aiofile uses caio (kernel AIO) which creates contexts in a global dict that are never cleaned up. Under concurrent execution these accumulate until the OS aio-max-nr limit is exhausted, causing SystemError(11, 'Resource temporarily unavailable'). aiofiles uses thread pools instead and does not have this issue.

Migrates all aiofile.async_open usages across both backend and lfx packages to aiofiles.open.

Based on #12433 by @manav2000, extended to cover all remaining usages.

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[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.39%. Comparing base (60713e3) to head (8a570e7).
⚠️ Report is 5 commits behind head on release-1.9.0.

Files with missing lines	Patch %	Lines
src/backend/base/langflow/initial_setup/setup.py	25.00%	3 Missing ⚠️
...rc/lfx/custom/directory_reader/directory_reader.py	33.33%	2 Missing ⚠️
...backend/base/langflow/services/flow/flow_runner.py	50.00%	1 Missing ⚠️
src/lfx/src/lfx/load/load.py	66.66%	1 Missing ⚠️
src/lfx/src/lfx/services/settings/base.py	50.00%	1 Missing ⚠️

❌ Your project status has failed because the head coverage (49.26%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@                Coverage Diff                @@
##           release-1.9.0   #12525      +/-   ##
=================================================
+ Coverage          50.37%   50.39%   +0.01%     
=================================================
  Files               1933     1937       +4     
  Lines             172918   172750     -168     
  Branches           26641    24219    -2422     
=================================================
- Hits               87112    87056      -56     
+ Misses             84732    84644      -88     
+ Partials            1074     1050      -24     

Flag	Coverage Δ
backend	55.91% <66.66%> (-0.05%)	⬇️
frontend	49.38% <ø> (+0.10%)	⬆️
lfx	49.26% <50.00%> (-0.31%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/backend/base/langflow/api/v1/flows_helpers.py	71.07% <100.00%> (ø)
...rc/backend/base/langflow/services/storage/local.py	74.59% <100.00%> (ø)
...backend/base/langflow/services/flow/flow_runner.py	78.47% <50.00%> (ø)
src/lfx/src/lfx/load/load.py	65.38% <66.66%> (ø)
src/lfx/src/lfx/services/settings/base.py	74.00% <50.00%> (ø)
...rc/lfx/custom/directory_reader/directory_reader.py	18.09% <33.33%> (ø)
src/backend/base/langflow/initial_setup/setup.py	53.92% <25.00%> (-2.07%)	⬇️

... and 208 files with indirect coverage changes

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[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	30.34% (32137/105907)	63.74% (4112/6451)	31.44% (750/2385)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
3182	0 💤	0 ❌	0 🔥	5m 40s ⏱️

[Cristhianzl]

lgtm