Consistent use of BIN_NAME in activation scripts

[dhruvmanila]

This PR fixes the bug where the BIN_NAME replacement field wasn't being used in the activator scripts.

fixes: #1518

Test plan

As I don't have a Windows machine, I switched the bin_name value here to point to Scripts on unix platform:

uv/crates/gourgeist/src/bare.rs

Lines 99 to 105 in 2a76c59

	let bin_name = if cfg!(unix) {
	"bin"
	} else if cfg!(windows) {
	"Scripts"
	} else {
	unimplemented!("Only Windows and Unix are supported")
	};

Code diff

```diff
diff --git a/crates/gourgeist/src/bare.rs b/crates/gourgeist/src/bare.rs
index 4c7808d3..0e0b41cf 100644
--- a/crates/gourgeist/src/bare.rs
+++ b/crates/gourgeist/src/bare.rs
@@ -97,9 +97,9 @@ pub fn create_bare_venv(location: &Utf8Path, interpreter: &Interpreter) -> io::R
     // TODO(konstin): I bet on windows we'll have to strip the prefix again
     let location = location.canonicalize_utf8()?;
     let bin_name = if cfg!(unix) {
-        "bin"
-    } else if cfg!(windows) {
         "Scripts"
+    } else if cfg!(windows) {
+        "bin"
     } else {
         unimplemented!("Only Windows and Unix are supported")
     };

I then created the virtual environment as usual and tested out that the path modifications were correct:

$ cargo run --bin uv -- venv
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s
     Running `target/debug/uv venv`
Using Python 3.12.1 interpreter at /Users/dhruv/.pyenv/versions/3.12.1/bin/python3.12
Creating virtualenv at: .venv

$ source .venv/Scripts/activate

$ echo $PATH
/Users/dhruv/work/astral/uv/.venv/Scripts:[...]

$ which python
/Users/dhruv/work/astral/uv/.venv/Scripts/python

I'm not sure how else to test this without having access to a Windows machine

[MichaReiser]

Could you expand the summary with a test plan?

[T-256]

Is this also fixes #1251?

[dhruvmanila]

@MichaReiser I updated the PR description with a test plan but, as I don't have a windows machine, it's a bit of a workaround which should test it in a way as expected on a windows machine.

Is this also fixes #1251?

Probably not, \cc @konstin who can confirm once he's back from his PTO on Monday.

[zanieb]

Is this how these look in the upstream activation scripts?

[dhruvmanila]

Is this how these look in the upstream activation scripts?

Yes, I basically copied from there. Sorry, I should've mentioned it in the PR description but here's an example from one of the activator script:

https://github.com/pypa/virtualenv/blob/fa283474fd199e3836f8b2c99510190c6b77e2bc/src/virtualenv/activation/bash/activate.sh#L55