feat: Add support for custom test attributes

[foresterre]

You may now add the attribute #[parameterized_macro(...)] after a #[parameterized(...)] attribute. The ... in the parameterized_macro may be replaced with a custom test attribute such as tokio::test.

As an additional treat (because the above would not half be as useful without some of these), the parameterized test function now also parses and provides codegen for the async, const and unsafe keywords, in addition to the also newly added support for specifying return types.

closes #80

[foresterre]

This is now supported and will be released as 2.0.0

Example usage:

parameterized/src/lib.rs

Lines 95 to 111 in e018621

	mod custom_test_attribute {
	use super::*;
	ide!();
	#[parameterized(input = { true, true, true })]
	#[parameterized_macro(tokio::test)]
	async fn tokio_simple_meta(input: bool) {
	assert!(input)
	}
	#[parameterized(input = { true, true, true })]
	#[parameterized_macro(tokio::test(flavor = "multi_thread", worker_threads = 1))]
	async fn tokio_complex_meta(input: bool) {
	assert!(input)
	}
	}