(fix):Implement cross-platform path formatting function

[corybsa]

Added a function to format paths for cross-platform compatibility. I am not well versed in Lua, please let me know if there is a better way to do this.

[sentry]

Bug: The format_path function creates a path in a tmp subdirectory relative to the current working directory, which is unlikely to exist on Windows, causing file operations to fail.
_{Severity: HIGH}

Suggested Fix

Instead of hardcoding a relative tmp directory, the code should be modified to use the system's actual temporary directory. Functions like vim.fn.tempname() or an equivalent method to get the OS-specific temp path (e.g., from the %TEMP% environment variable on Windows or /tmp on Unix-like systems) should be used to ensure temporary files are created in a valid, writable location.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: lua/99/utils.lua#L19-L21

Potential issue: The `format_path` function constructs a file path by joining components
with the platform-specific separator. On Windows, this results in a path like
`C:\Users\...\tmp\99-1234`. The code attempts to create a file in a `tmp` subdirectory
relative to the current working directory. This `tmp` directory is not a standard
Windows temporary location and is unlikely to exist, which will cause subsequent file
operations like `io.open()` to fail. The intended behavior was likely to use the
system's designated temporary directory.

_{Did we get this right? 👍 / 👎 to inform future reviews.}