Improve range checking

[xin9le]

Summary

This pull request refactors the implementation of range checks in the IsDefined(T value) method for enum types in UnderlyingOperation.cs and its code generator template. The main improvement is replacing the previous two-comparison check for continuous enums with a more efficient single unsigned comparison that leverages wraparound semantics. This change is applied consistently across all relevant numeric types.

Benchmark results

Approximately x1.05 faster.

BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8737/25H2/2025Update/HudsonValley2)
Intel Core Ultra 7 155H 3.00GHz, 1 CPU, 22 logical and 16 physical cores
.NET SDK 10.0.301
  [Host]     : .NET 10.0.9 (10.0.9, 10.0.926.27113), X64 RyuJIT x86-64-v3
  DefaultJob : .NET 10.0.9 (10.0.9, 10.0.926.27113), X64 RyuJIT x86-64-v3


| Method            | Mean     | Error    | StdDev   | Median   | Ratio | RatioSD | Allocated | Alloc Ratio |
|------------------ |---------:|---------:|---------:|---------:|------:|--------:|----------:|------------:|
| RangeCheck_Simple | 31.21 ns | 1.060 ns | 3.077 ns | 30.02 ns |  1.01 |    0.14 |         - |          NA |
| RangeCheck_Cast   | 29.82 ns | 0.779 ns | 2.296 ns | 29.59 ns |  0.96 |    0.12 |         - |          NA |

[Copilot]

Pull request overview

This pull request refactors UnderlyingOperation<T>.IsDefined(T value) for continuous enums to use a single unsigned wraparound comparison instead of two ordered comparisons, aiming to improve performance (notably for hot-path IsDefined calls).

Changes:

• Updated the T4 template (UnderlyingOperation.tt) to generate a single unsigned range check based on (val - min) <= (max - min) wraparound semantics.
• Updated the generated implementation (UnderlyingOperation.cs) across all underlying numeric types to use the new range-check pattern.
• Added explanatory inline comments describing the wraparound-based approach.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libs/FastEnum.Core/Internals/UnderlyingOperation.tt	Updates the generator template to emit the new single unsigned wraparound range-check logic.
src/libs/FastEnum.Core/Internals/UnderlyingOperation.cs	Applies the generated wraparound range-check logic to each underlying-type specialization of IsDefined.

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