fix(memory-storage): Avoid duplicate processed requests in memory request queue client

[vdusek]

Description

• MemoryRequestQueueClient.add_batch_of_requests appended a ProcessedRequest twice for requests that were already present in the queue but not yet handled — once in the was_already_present branch and again at the unconditional append after the if/else block, which that branch did not skip.
• This violated the contract that AddRequestsResponse.processed_requests contains exactly one entry per input request and inflated results for any caller iterating the list.
• Removed the inner append so the shared append at the end handles both branches, matching the structure of the file system client. Added a regression test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.89%. Comparing base (dc1ed61) to head (1577ff2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1941      +/-   ##
==========================================
+ Coverage   92.85%   92.89%   +0.04%     
==========================================
  Files         167      167              
  Lines       11714    11713       -1     
==========================================
+ Hits        10877    10881       +4     
+ Misses        837      832       -5     

Flag	Coverage Δ
unit	92.89% <ø> (+0.04%)	⬆️

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[Mantisus]

LGTM