Better perfdata parsing and other improvements

[inqrphl]

Perfdata related improvements

• Add explanations to the regexes used in the parser
• Use '' when specifying all non-special characters in the regex, including capture fields. No need to concern if a comma, semicolon etc. is a special character
• Convert some German leftover names to English
• Add example value of perfdata string regex match
• Use Enum to browse perdata fields like Value, UOM, Warn, Crit, Min, Max instead of a string keyed map, clearer to read
• Revise the perdata reading logic, use guards and skip early where possible instead of adding more nested code
• Add max length filters to each field of the perfdata: value, uom, warn, crit, min, max , the max lengths are configurable from the config line
• Move config parsing of NagiosSpoolfiles from main function to nagiosCollectorFactory. Main function only parses to check if its enabled, the factory looks through the config. Removes clutter from the main function.
• Once perfdata values are read from the passed SERVICEPERFDATA, a regex is used to extract different perfdata groups and fields. After the regex match, concatenate the raw matches and see if it makes up the original string. This finds cases where non-digit characters were hanging after the Min value of the last perfdata group

General improvements

• Fix package structure, now each module is under github.com/ConSol-Monitoring/nagflux/ .
• No need to use rewrite hacks in go.mod . This also fixes the problem where the package itself had to be vendored since building nagflux did not use sources under pkg/ , it wrongly used the vendored nagflux sources under vendor/
• Update to golang 1.26.1 , update dependencies including the vulnerable sys package
• Update golangci lint to 2.11.3 , removes some false positives

[inqrphl]

Reviewed changes that happened due to package renaming, file moving or golangci-lint updates.

Important changes are in other files