Implement pip dependency caching for Azure Pipelines

[unnatikdm]

## Description
Implements pip dependency caching for Azure Pipelines to reduce CI runtime (Issue #5255)

## Changes Made

### 1. Dynamic Cache Path Configuration
Added platform-specific cache path detection:
- **Linux/macOS**: `$(HOME)/.cache/pip`
- **Windows**: `$(LocalAppData)\pip\Cache`

```yaml
- bash: |
    if [ "$(Agent.OS)" == "Windows_NT" ]; then
      echo "##vso[task.setvariable variable=PIP_CACHE_DIR]$(LocalAppData)\pip\Cache"
    else
      echo "##vso[task.setvariable variable=PIP_CACHE_DIR]$(HOME)/.cache/pip"
    fi
  displayName: 'Set pip cache directory'

2. Cache@2 Task Integration

Added the caching task to save/restore pip dependencies:

- task: Cache@2
  inputs:
    key: 'pip | "$(Agent.OS)" | "$(PYTHON_VERSION)" | "$(BUILD_TYPE)" | "$(imageName)" | **/requirements.txt'
    restoreKeys: |
      pip | "$(Agent.OS)" | "$(PYTHON_VERSION)" | "$(BUILD_TYPE)" | "$(imageName)"
      pip | "$(Agent.OS)" | "$(PYTHON_VERSION)" | "$(BUILD_TYPE)"
      pip | "$(Agent.OS)" | "$(PYTHON_VERSION)"
    path: $(PIP_CACHE_DIR)
  displayName: 'Cache pip dependencies'

Testing Done

• ✅ Verified cache works on Linux
• ✅ Verified cache works on Windows
• ✅ Confirmed cache hits on subsequent runs
• ✅ Tested cache isolation across Python versions
• ✅ Validated fallback keys work

Related

Closes #5255

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.82%. Comparing base (900d20b) to head (855f366).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5267      +/-   ##
===========================================
- Coverage    93.83%   93.82%   -0.01%     
===========================================
  Files          180      180              
  Lines        22473    22473              
  Branches      3189     3189              
===========================================
- Hits         21088    21086       -2     
- Misses         923      924       +1     
- Partials       462      463       +1     

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