fix: validate new prefix length against old prefix

[maurosilber]

Description

If the target prefix is larger than the placeholder prefix, it would overwrite into other regions of the binary truncate the prefix. It would likely lead to broken binaries: https://discord.com/channels/1082332781146800168/1212673297347518464/1450859607072182374

Possible issue outside rattler

Being a public function, this function might be being used outside rattler in some valid ways that would now return an error. For example, relocating an environment:

1. On installation, the new prefix is not longer than the old prefix (the build prefix placeholder) -> ✅
2. On relocation, the new prefix is longer than the old prefix (but not longer that the build prefix placeholder) -> returns an error although it would be correct.

Alternatives

It might be more "rustic" to encode this restriction into a type such as:

struct PlaceholderChange {
    old_placeholder: &str,
    new_placeholder: &str,
}

pub fn copy_and_replace_cstring_placeholder(
    mut source_bytes: &[u8],
    mut destination: impl Write,
    placeholder_chance: PlaceholderChange,
) -> Result<(), std::io::Error>

instead of accepting any placeholders:

pub fn copy_and_replace_cstring_placeholder(
    mut source_bytes: &[u8],
    mut destination: impl Write,
    prefix_placeholder: &str,
    target_prefix: &str,
) -> Result<(), std::io::Error>

but would be a breaking change in a public function.

Also, it would not solve the relocation use case (for which I have an idea that would imply changing the info/has_prefix file, which would be an even bigger breaking change in the conda ecosystem not work after thinking about it some more).

[wolfv]

Thank you @maurosilber!