fix(cli): fixed runtime metadata filename not being valid (special characters) for all platforms

[EduardWayland]

This PR should solve the issue #1318.
I have noticed that in the latest version of Genkit (0.9.X), the filename of runtime follows the format ${process.pid}-${timestamp}.json as in the writeRuntimeFile(). However, the produced filename is not a valid name on Windows due to the timestamp part which contains reserved characters such as ":".

What happens next is that when you try to run any kind of script using genkit library, the runtime file won't be generated due to
invalid filename: "Error writing runtime file: Error: ENOENT: no such file or directory, open '.genkit\runtimes\42744-2024-11-18T12:17:25.549Z.json'

As I don't know exactly the purpose of the ISO format in the filename, I've replaced that format with the milliseconds.

Checklist (if applicable):

• Tested (manually, unit tested, etc.)
• Changelog #updated
• Docs updated

[pavelgj]

Thanks for the fix! LGTM