[CuddlesPrime]

With an Iris shader pack, Veil shaders drawn through ShaderWrapperMixin break GUIs and don't show up (e.g. Create: Aeronautics' Hot Air Burner flame).

Problems

• Iris's framebuffer is never unbound. @Share("drawn") doesn't carry from apply() to clear() (they're different methods), so AdvancedFbo.unbind() never runs. In GUIs, everything drawn afterwards goes offscreen (Aeronautics ponders and inventory items).
• Wrong colortex0 copy. The simple framebuffer always uses colortex0's main texture, but packs that flip colortex0 (e.g. Complementary) draw the world into the alt one, so the draw is lost.
• Redirects too often. It also redirects in GUIs and during the shadow pass.

Fix

In ShaderWrapperMixin (NeoForge and Fabric):

• Save the bound framebuffers in apply and restore them in clear.
• Redirect only when shouldOverrideShaders() is true and it isn't the shadow pass, matching Iris's own handling of unknown shaders.
• Use IrisRenderingPipeline.bindDefault(), which picks the correct colortex0 copy.

IrisRenderingPipelineMixin and IrisRenderingPipelineExtension are no longer used and are removed.