[Fix] varying bug when using @interpolate

[samw-improbable]

Description

If you try to use a type that requires flat interpolation (e.g. u32) then you will get browser errors saying you need to add @interpolate(flat). If you add this though, this got included in the var<private> line (i.e. varying @interpolate(flat) myValue: u32 -> var<private> @interpolate(flat) myValue: u32), which resulted in a WGSL compilation error.

This PR updates the regex to pull out the type as well as the name, and then constructs the var<private> lines from that, rather than reusing the entire matched line, to avoid the syntax error.

Checklist

• I have read the contributing guidelines
• My code follows the project's coding standards
• This PR focuses on a single change

[Copilot]

Pull Request Overview

This PR fixes a WGSL compilation error that occurred when using @interpolate attributes with varying declarations. The issue was that the entire varying declaration line (including interpolation attributes) was being reused in var<private> declarations, which caused syntax errors since attributes are not allowed in private variable declarations.

Key Changes:

• Updated the VARYING regex to capture both the variable name and type
• Modified the private variable declaration to reconstruct the line from captured name and type only, excluding interpolation attributes

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[Copilot]

The regex pattern [\w<>]+ for capturing the type is too permissive and will not correctly handle nested generic types or array types with dimensions (e.g., vec3<f32> or array<vec4<f32>, 4>). Consider using a more robust pattern like [\w<>,\s\d]+ to properly capture complex type syntax including spaces, commas, and numbers in type parameters.

Suggested change

	const VARYING = /(?:@interpolate\([^)]*\)\s*)?([\w]+)\s*:\s*([\w<>]+)/;
	const VARYING = /(?:@interpolate\([^)]*\)\s*)?([\w]+)\s*:\s*([\w<>,\s\d]+)/;