Test: support do-block syntax in @test_throws

[christiankadiu]

I am opening this PR because I have identified the following issue:
Currently, using a do block with the @test_throws macro fails silently or behaves unexpectedly. For example:

@test_throws(ErrorException) do
    error("This should pass but it fails")
end

Because do blocks are parsed as anonymous functions passed as the first argument to the macro, @test_throws receives the expression as a closure (e.g., () -> begin ... end) and simply evaluates it. Since evaluating a closure definition only returns the function without executing its body, no exception is ever thrown, leading to a test failure.
This PR introduces explicit support for do-block syntax in @test_throws. It inspects the AST to detect if the passed expression is a zero-argument anonymous function (checking for :-> or :function heads with empty argument tuples). If it is, the macro rewrites the AST to wrap the escaped expression in an Expr(:call, ...) so that the closure is actually executed during the test.
This provides a much-needed quality of life improvement for testing longer blocks of code that are expected to throw exceptions.

[halleysfifthinc]

Can you elaborate on the quality-of-life benefits of this new syntax, in comparison to the already working begin-block style? None of the other @test_* macros support the do-block syntax.

@test_throws ErrorException begin
    error("This should pass but it fails")
end