fix: Prevent race condition in concurrent storage creation

[Mantisus]

Description

• Fix race condition when concurrent creating storage.

Issues

• Closes: Dataset get_data() returns fewer items than successfully pushed with context.push_data() in PlaywrightCrawler #1621

Testing

• Add new tests for StorageInstanceManager

[codecov]

Codecov Report

❌ Patch coverage is 93.02326% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.46%. Comparing base (30f8e15) to head (5183f2c).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
src/crawlee/storages/_storage_instance_manager.py	93.02%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1626      +/-   ##
==========================================
- Coverage   92.48%   92.46%   -0.02%     
==========================================
  Files         157      157              
  Lines       10421    10437      +16     
==========================================
+ Hits         9638     9651      +13     
- Misses        783      786       +3     

Flag	Coverage Δ
unit	92.46% <93.02%> (-0.02%)	⬇️

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[janbuchar]

Nice catch!

[vdusek]

Thanks!