fix: Prevent KeyError in AWSClient on lock timeout

[sentry]

This PR addresses the KeyError: 'secretsmanager' occurring in ddpui/utils/aws_client.py.

Problem:
The AWSClient._get_client method was susceptible to a KeyError when multiple concurrent requests attempted to initialize an AWS client (e.g., 'secretsmanager'). The _clients dictionary was initialized as empty. If a thread failed to acquire the service-specific lock within the 10-second timeout, it would proceed to access cls._clients[service_name] without service_name being guaranteed to exist in the dictionary, leading to a KeyError.

Solution:

1. Pre-initialize _clients: The _clients class variable is now initialized with None values for all SUPPORTED_SERVICES. This ensures that all expected service keys are present in the dictionary from the start, preventing KeyError when attempting to access cls._clients[service_name].
2. Fail fast on lock timeout: If threading.Lock().acquire() times out, a RuntimeError is now explicitly raised. This prevents the execution from proceeding with an uninitialized client and provides clearer error messaging.
3. Update reset_instance: The reset_instance method now also re-initializes _clients with None values for all supported services, maintaining consistency with the class's initial state.

Fixes DALGO-BACKEND-2AJ

[sentry]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.66%. Comparing base (75cb6fd) to head (e402db4).

Files with missing lines	Patch %	Lines
ddpui/utils/aws_client.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1380   +/-   ##
=======================================
  Coverage   58.66%   58.66%           
=======================================
  Files         132      132           
  Lines       15690    15690           
=======================================
  Hits         9205     9205           
  Misses       6485     6485           

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