clean up shader cache errors

[atlv24]

Objective

• Name error type more accurately, its about the shader cache not pipeline cache.
• Put naga error in Box to make type smaller and clippy happy

Solution

• do it

Testing

• examples run

[kfc35]

if i understand correctly, the change to box the error doesn’t change anything with how #[error(transparent)] outputs, so this should be ok, but someone can double check me on this