Add environment variable configuration for BatchAsyncContainerExecutor MaxOperationsInDirectModeBatchRequest

[Copilot]

This PR adds the ability to customize the MaxOperationsInDirectModeBatchRequest used by BatchAsyncContainerExecutor through environment variable configuration, as requested in the issue.

Changes Made

🆕 New Features

• Environment Variable Support: Added COSMOS_MAX_OPERATIONS_IN_DIRECT_MODE_BATCH_REQUEST environment variable
• Backward Compatibility: Falls back to existing Constants.MaxOperationsInDirectModeBatchRequest when env var is not set
• Input Validation: Validates positive integer values and provides clear error messages for invalid inputs

📁 Files Added/Modified

1. BatchConfiguration.cs (New) - Configuration helper class with environment variable support
2. BatchAsyncContainerExecutorCache.cs - Updated to use configurable value (minimal 1-line change)
3. BatchConfigurationTests.cs (New) - Comprehensive unit tests
4. BatchAsyncContainerExecutorCacheTests.cs - Added integration test

🔧 Usage Example

# Set custom batch operation limit
export COSMOS_MAX_OPERATIONS_IN_DIRECT_MODE_BATCH_REQUEST=200

# Cosmos DB client will now use 200 operations per batch instead of default
CosmosClient client = new CosmosClient(connectionString, new CosmosClientOptions 
{ 
    AllowBulkExecution = true 
});

✅ Implementation Details

• Environment Variable Name: COSMOS_MAX_OPERATIONS_IN_DIRECT_MODE_BATCH_REQUEST
• Expected Values: Positive integers (e.g., "50", "200", "500")
• Default Behavior: Uses existing constant value when env var not set
• Error Handling: Throws ArgumentException with descriptive messages for invalid values

🧪 Testing

Added comprehensive test coverage including:

• Default behavior (no environment variable)
• Custom values from environment variable
• Input validation (negative numbers, invalid strings, zero)
• Edge cases (empty strings, large values)
• Integration testing with BatchAsyncContainerExecutorCache

🛡️ Quality Assurance

• Minimal Changes: Only 1 line modified in existing production code
• No Breaking Changes: Existing behavior preserved when env var not set
• Build Verified: Project builds successfully
• Backward Compatible: Existing tests and functionality unaffected

This implementation provides enterprise-ready configurability for batch operations while maintaining the robustness and reliability of the existing codebase.

Fixes #5294.

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[kirankumarkolli]

Move to ConfigurationManager as method

[Copilot]

Moved the logic to ConfigurationManager.GetMaxOperationsInDirectModeBatchRequest() method as requested. The BatchConfiguration class now delegates to this centralized configuration method. (8abde21)

[kirankumarkolli]

Remove BatchConfiguration class, its unnecessary

[Copilot]

Removed the unnecessary BatchConfiguration class as requested. The logic is now handled directly by ConfigurationManager.GetMaxOperationsInDirectModeBatchRequest() and the wrapper class has been eliminated. Tests have been updated to test ConfigurationManager directly. (00ea126)

[kirankumarkolli]

Valid only if value is less than Constants.MaxOperationsInDirectModeBatchRequest and positive

[Copilot]

Added validation to ensure the value is positive and less than or equal to Constants.MaxOperationsInDirectModeBatchRequest. Updated tests accordingly. (8abde21)

[kirankumarkolli]

Its reading everytime and checking ENVIRONMENT variables which is expensive.
Please read it once and use afterewards

[Copilot]

Implemented caching to read environment variable only once using Lazy<T>. The value is now cached on first access and reused for subsequent calls, eliminating the performance overhead. Added test-friendly controls to disable caching during unit tests. (d515dd8)

[kirankumarkolli]

Suggested change

	internal static readonly string MaxOperationsInDirectModeBatchRequest = "COSMOS_MAX_OPERATIONS_IN_DIRECT_MODE_BATCH_REQUEST";
	internal static readonly string MaxOperationsInDirectModeBatchRequest = "AZURE_COSMOS_MAX_OPERATIONS_IN_BATCH_REQUEST";

[Copilot]

Updated environment variable name to "AZURE_COSMOS_MAX_OPERATIONS_IN_BATCH_REQUEST" as suggested and updated corresponding tests. (d515dd8)