Fix critical bugs and improve code quality in processenv2

[Copilot]

This PR addresses multiple critical issues found in the processenv2 codebase that were causing 8 test failures and significant code quality problems.

Issues Fixed

1. Equals Sign Handling in Values

The previous implementation incorrectly split environment variable values on all = characters, breaking values like TEST=YG==:

// Before: splitVal = val.split('=')  // ["TEST", "YG", "", ""]
// After: Proper substring extraction
const firstEquals = val.indexOf('=');
const value = val.substring(firstEquals + 1);  // "YG=="

2. Quotation Mark Processing

Fixed quotation mark removal to preserve inner quotes while removing only outer ones:

# Before: TEST='"Some Text"' → "Some Text" (inner quotes removed)
# After: TEST='"Some Text"' → "Some Text" (inner quotes preserved)

3. Variable Substitution Support

Extended regex pattern to support lowercase and numeric variable names:

// Before: /\${[A-Z_]+}/g  // Only uppercase
// After: /\${[A-Za-z_][A-Za-z0-9_]*}/g  // Supports lowercase, numbers

4. Escape Sequence Handling

Implemented proper escape sequence processing for \n, \\, etc.:

TEST=Some Text\nMore Text  # Now correctly converts to actual newline
TEST=Some Text\\More Text  # Now correctly converts to single backslash

5. Comment Detection Logic

Improved hashtag handling to distinguish between values containing # and actual comments:

TEST=Some Text#More Text     # Hashtag preserved as part of value
TEST=Some Text # comment     # Comment properly filtered out

Code Quality Improvements

• Formatting: Fixed replaceNestedChars.js which was completely unformatted (single line)
• Documentation: Enhanced JSDoc comments with complete parameter descriptions
• Input Validation: Added type checking and error handling throughout
• Error Handling: Added try-catch blocks for file operations with proper warnings

Test Results

• ✅ All 25 tests now pass (previously 8 failing)
• ✅ No ESLint errors or warnings
• ✅ Maintained high code coverage

The library now correctly handles all documented features and edge cases, making it more robust and reliable for production use.

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[Nexus633]

fix