Add comprehensive test coverage for token generator/validator

[Copilot]

Addresses missing test scenarios in the token package identified during code review of PR #40.

Added Test Coverage

• Empty/whitespace token validation - Verifies ErrTokenEmpty for empty and whitespace-only inputs
• Invalid encoding formats - Tests malformed base64 (invalid characters, padding) and hex strings (non-hex chars, odd-length)
• GenerateBytes() method - Validates raw byte generation with default and custom minBytes configurations
• Invalid configuration values - Tests negative/zero values for minEntropyBits, minBytes, and maxLength return ErrInvalidTokenConfig
• Token randomness - Ensures consecutive generations produce unique tokens and byte sequences
• Invalid encoding enum - Tests out-of-range TokenEncoding values

All tests follow existing package patterns and use bytes.Equal() for efficient byte comparison.

// Example test ensuring tokens are cryptographically random
func TestTokenRandomness(t *testing.T) {
    generator, err := NewGenerator()
    token1, _ := generator.Generate()
    token2, _ := generator.Generate()
    
    if token1 == token2 {
        t.Fatalf("expected different tokens, got identical: %s", token1)
    }
}

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[Copilot]

Pull request overview

This pull request adds comprehensive test coverage for the token generator/validator package to address gaps identified in PR #40. The tests validate error handling for edge cases, configuration validation, encoding formats, and cryptographic randomness.

Changes:

• Added 15 new test functions covering empty/whitespace validation, invalid encoding formats, raw byte generation, invalid configuration values, token randomness, and invalid encoding enums
• Added bytes package import for efficient byte slice comparison in randomness tests

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[Copilot]

Variable name 'bytes' shadows the imported 'bytes' package. Consider renaming to 'data', 'result', or 'tokenBytes' to avoid confusion and potential issues if the bytes package methods need to be used later in this function.

[Copilot]

Variable name 'bytes' shadows the imported 'bytes' package. Consider renaming to 'data', 'result', or 'tokenBytes' to avoid confusion and potential issues if the bytes package methods need to be used later in this function.