refactor(parser): handle exp and redirect in inspect mode

[dmotylev]

Refactored SPF parser to ensure exp and redirect are not ignored
in inspect mode. Introduced separate observe and evaluate functions
to structure token processing. Added conditions to handle directive
registration without execution in inspect mode.

[Copilot]

Pull Request Overview

This PR refactors the SPF parser to better handle the "exp" and "redirect" mechanisms in inspect mode by introducing separate observe and evaluate functions and adjusting the processing logic.

• Introduces observe and evaluate functions for token processing
• Adjusts handling of inspect mode by bypassing execution of redirection in favor of logging its presence
• Minor update to error messaging in parseVersion and handleRedirect functions

Comments suppressed due to low confidence (1)

parser.go:286

• [nitpick] The error returned by handleExplanation is ignored. Consider checking and handling the error to ensure that issues during explanation processing are not silently skipped.

exp, _ := p.handleExplanation(token)