Ruby 3.2 compatibility and some minor tweaks.

[boof]

Hi there,

the gemspec required an update as Ruby 3.2 dropped support for File.exists? in favor of File.exist? which existed since <= mri v1.8.7, too.

Also reduced the number of objects being generated during log parsing by moving them into constants. This could benefit high volume setups.

Feel free to take any of the changes I made.

Cheers boof