Add analyzer to detect HasFlag() and suggest HasFlagFast() replacement - #199

Implements analyzer NEEG005 to detect HasFlag() calls on enums with [EnumExtensions] or [EnumExtensions<T>] attributes and suggest replacing with the generated HasFlagFast() extension method for better performance.

Implementation

• HasFlagAnalyzer: Detects HasFlag() invocations on qualifying enums at Information severity level
• HasFlagCodeFixProvider: Replaces HasFlag() with HasFlagFast(), supports batch fixing
• Follows existing patterns from ToStringAnalyzer and ToStringCodeFixProvider

Example

[EnumExtensions]
[Flags]
public enum FilePermissions 
{
    Read = 1,
    Write = 2,
    Execute = 4
}

// Before
if (permissions.HasFlag(FilePermissions.Read))  // NEEG005: Use HasFlagFast()

// After fix
if (permissions.HasFlagFast(FilePermissions.Read))

Test Coverage

• 17 test cases covering decorated enums, external enums via [EnumExtensions<T>], non-decorated enums, and various invocation contexts
• Verified no regressions in existing analyzer tests

• Fixes Create analyzer to detect usages of HasFlag() and suggest replacing with HasFlagFast() #188

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