Extract clamp methods to MathUtils

[Glavo]

1. 调整 clamp 方法的参数顺序，与 Java 21 中 Math 类新添加的 clamp 方法保持一致；
2. 将 clamp 方法提取到 MathUtils 类中，避免未来我们反向移植补丁时因为参数顺序造成隐蔽的问题。

[Copilot]

Pull request overview

This PR standardizes clamping utilities by moving them out of Lang into a dedicated MathUtils class and switching the parameter order to match Java 21’s Math.clamp, reducing the risk of subtle bugs during future backports.

Changes:

• Added MathUtils with clamp(value, min, max) overloads for int and double.
• Removed the old Lang.clamp(...) overloads.
• Updated UI call sites to use MathUtils.clamp(...) with the new argument order.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
HMCLCore/src/main/java/org/jackhuang/hmcl/util/MathUtils.java	Introduces the new centralized clamp helpers with Java 21-style parameter order.
HMCLCore/src/main/java/org/jackhuang/hmcl/util/Lang.java	Removes the legacy clamp methods to avoid future accidental usage with the old argument order.
HMCL/src/main/java/org/jackhuang/hmcl/ui/decorator/DecoratorController.java	Migrates background opacity clamping to MathUtils.clamp(value, min, max).
HMCL/src/main/java/org/jackhuang/hmcl/ui/construct/FloatScrollBarSkin.java	Migrates scrollbar value clamping to MathUtils.clamp(value, min, max).

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[Copilot]

assert min <= max will be skipped when assertions are disabled (typical in production), so invalid ranges can silently produce incorrect results. If the intent is to align with Java 21 Math.clamp, consider doing an explicit runtime check and throwing IllegalArgumentException when min > max (also covers NaN for the double overload if you use !(min <= max)).

Suggested change

	assert min <= max;
	return Math.min(max, Math.max(value, min));
	}
	/// Clamp value to fit between min and max.
	public static int clamp(int value, int min, int max) {
	assert min <= max;
	if (!(min <= max)) {
	throw new IllegalArgumentException("min must be less than or equal to max");
	}
	return Math.min(max, Math.max(value, min));
	}
	/// Clamp value to fit between min and max.
	public static int clamp(int value, int min, int max) {
	if (min > max) {
	throw new IllegalArgumentException("min must be less than or equal to max");
	}