Function validate_alignment_precision 

pub fn validate_alignment_precision(spec: &FieldSpec, value: &str) -> bool

Validate alignment+precision constraints for string fields Returns false if validation fails (should reject the match)

This validates the constraints described in issue #3 (parse#218):

• Fill characters should only be in correct positions (left for right-align, right for left-align)
• Total width (including fill chars) should not exceed specified width when width is specified
• Content length (after removing fill chars) should not exceed precision