Refactor: Introduce EnvManager for structured environment variable handling

[Kyle-Ye]

Summary

Introduces a comprehensive EnvManager system to replace the simple envEnable() function with structured, testable, and maintainable environment variable management.

Key Features

1. Domain-based Variable Lookup

• Automatically searches for domain-prefixed environment variables (e.g., OPENATTRIBUTEGRAPH_*, OPENSWIFTUI_*)
• Supports fallback to raw key with includeFallbackToRawKey option
• Cleaner variable names: DEVELOPMENT instead of OPENATTRIBUTEGRAPH_DEVELOPMENT

2. Multiple Value Types

• envBoolValue() - Boolean environment variables (0/1)
• envIntValue() - Integer environment variables
• envStringValue() - String environment variables
• All return optional types for better error handling

3. Testability & Flexibility

• Custom environment provider support via EnvironmentProvider protocol
• reset() method for test cleanup
• withDomain() for temporary domain contexts
• Dependency injection ready

4. Enhanced Debugging

• Automatic logging of environment variable resolution
• Shows which key was checked and the resolved value
• Displays when default values are used

Environment Variable Changes

All environment variables now use shorter names with automatic domain prefixing:

Old Name	New Name	Notes
OPENATTRIBUTEGRAPH_DEVELOPMENT	DEVELOPMENT	Searches OPENATTRIBUTEGRAPH_*, OPENSWIFTUI_*
OPENATTRIBUTEGRAPH_WERROR	WERROR	Domain-based search
OPENATTRIBUTEGRAPH_LIBRARY_EVOLUTION	LIBRARY_EVOLUTION	Domain-based search
OPENATTRIBUTEGRAPH_COMPATIBILITY_TEST	COMPATIBILITY_TEST	Domain-based search
OPENATTRIBUTEGRAPH_USE_LOCAL_DEPS	USE_LOCAL_DEPS	Domain-based search
OPENATTRIBUTEGRAPH_ATTRIBUTEGRAPH	ATTRIBUTEGRAPH	Domain-based search

Benefits

• ✅ More maintainable and testable code
• ✅ Better debugging with automatic logging
• ✅ Type-safe value parsing with optional types
• ✅ Flexible domain-based search with fallback options
• ✅ Supports nested domain contexts with withDomain()
• ✅ Backward compatible through domain-based search

Testing

• Package builds successfully with various environment variable configurations
• Both old (fully-qualified) and new (short) variable names work

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 4.87%. Comparing base (21426f2) to head (7a9d9d8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #194   +/-   ##
=====================================
  Coverage   4.87%   4.87%           
=====================================
  Files         28      28           
  Lines        820     820           
=====================================
  Hits          40      40           
  Misses       780     780           

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