🐛Fix "literal not terminated" error for markers with unpaired backticks in Pattern

[dongjiang1989]

Summary

Fixes the scanner error "literal not terminated" when parsing markers that contain an unpaired backtick in their pattern values, such as:

  // +kubebuilder:validation:items:Pattern=^[`a-zA-Z]+$                                                                                                      

Closes: #1084

Changes

1. pkg/markers/parse.go - Modified parserScanner function to:
   - Only enable ScanRawStrings when the input contains an even (balanced) number of backticks
   - Fix type conversion: scanner.Mode = uint(mode) to resolve compilation error
2. pkg/markers/parse_internal_test.go ( add new file) - Added test cases covering:
   - Single backtick pattern
   - Full "+kubebuilder:validation:items:Pattern=^[a-zA-Z]+$`" marker
   - Two backticks (balanced)
   - Three backticks (unbalanced)
   - Empty string (zero backticks)

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