Type errors trigger panics instead of generating Errors

[paulcadman]

Type errors in vamp-ir files cause panics instead of returning an Error to the caller. This is relevant when vamp-ir is being used as a library, for example by Taiga.

See the (currently ignored) test for an example:

vamp-ir/src/halo2/api.rs

Lines 202 to 207 in ed24c69

	#[test]
	#[ignore] // This test panics in type checking
	fn test_compile_type_error() {
	let config = Config { quiet: true };
	assert!(compile("(1, 2) = 1;", &config).is_err());
	}

To fix this issue we need to remove the .unwrap() calls in typecheck.rs, for example:

vamp-ir/src/typecheck.rs

Line 515 in bac5731

unify_types(expr_var, &Type::Int, types, &mut None).unwrap();