Use R_ParseEvalString in test

[CGMossa]

In a comment, it is stated that we'd ideally use R_ParseEvalString if we could.
Years has passed, and now all the supported versions of R contains R_ParseEvalString.
Replaced the test with it.

kevin@pop-os:~/GitHub/libR-sys$ rg -l R_ParseEvalString ./bindings/
./bindings/bindings-windows-x86_64-R4.3.rs
./bindings/bindings-macos-aarch64-R4.3.rs
./bindings/bindings-macos-aarch64-R4.2.rs
./bindings/bindings-linux-x86_64-R4.3.rs
./bindings/bindings-macos-x86_64-R4.3.rs
./bindings/bindings-linux-aarch64-R4.3.rs
./bindings/bindings-macos-x86_64-R4.2.rs
./bindings/bindings-linux-x86_64-R4.4-devel.rs
./bindings/bindings-linux-x86_64-R4.2.rs
./bindings/bindings-linux-aarch64-R4.2.rs
./bindings/bindings-linux-aarch64-R4.4-devel.rs
./bindings/bindings-windows-x86_64-R4.4-devel.rs
./bindings/bindings-macos-x86_64-R4.4-devel.rs
./bindings/bindings-windows-x86_64-R4.2.rs

[CGMossa]

I don't know why this is passing tests.

If I run this

#[test]
fn test_parse_eval_string() {
    with_r(|| unsafe {
        let bad_code = cstr!("c(10,42,20)");
        let bad = Rf_protect(R_ParseEvalString(bad_code.as_ptr(), R_GlobalEnv));
        Rf_PrintValue(bad);
        println!("Did we get here?");
        Rf_unprotect(1);
    });
}

[1] 10 42 20
Did we get here?
test test_parse_eval_string ... ok

But then

        let bad_code = cstr!("c(10,,42,20)");
        let bad = Rf_protect(R_ParseEvalString(bad_code.as_ptr(), R_NilValue));
        Rf_PrintValue(bad);
        println!("Did we get here?");
        Rf_unprotect(1);

running 1 test
Error: 'rho' must be an environment not NULL: detected in C-level eval
Fatal error: unable to initialize the JIT

error: test failed, to rerun pass `-p extendr-api --test parse_tests`

So the second argument to R_ParseEvalString must be R_GlobalEnv or something.
But that's not what is in this PR right now.

[Ilia-Kosenkov]

It could be that c() is a call to a function, and you need an environment to look it up. But you do not need one if you just evaluate a constant 1.