Final classes, custom sanitization defaults & phpinfo() flags

Breaking changes

• PhpInfo and SensitiveValueSanitizer are now final - they're security-related and not designed to be extended (#27)

New features

• Custom default sanitization replacement string via new SensitiveValueSanitizer('[REDACTED]') (#26)
• getHtml() and getFullPageHtml() now accept $flags parameter to control phpinfo() output sections (#21 & #23, thanks @compwright)
• addSanitization() annotated as @param non-empty-string to clarify the contract (#28) (removed in 2.0.1)

Internal changes

• Add phpstan/phpstan-strict-rules (#24)
• Bump actions/checkout from 5 to 6 (#20)
• Add CLAUDE.md (#22)
• Use use for all functions for those free extra nanoseconds (#25)
• Correct the path in the inline styles comment (#29)