Regex_Search: Add tokenizer, postfix conversion, and NFA construction

[AbhishekRai456]

Adds regex tokenizer with support for:

• Literals, operators, grouping and anchors (^, $)
• Character classes with ranges and shorthands (\d, \w, \s and negations)
• Quantifiers {m,n}, {m,}, {,n}, {m}
• Implicit concatenation insertion
• Error reporting with position tracking

Adds infix → postfix (RPN) conversion for regex tokens:

• Enforces operator precedence and associativity
• Performs syntax validation during conversion (invalid operators, mismatched parentheses, trailing operators)

Adds ε-NFA core representation (Nfa.hpp) and Thompson-style NFA construction (NfaBuilder.hpp):

• Manages state ownership internally with safe lifetime guarantees

This is a draft for review.

[Ovetsarilish]

Also, the match method which the user uses as an API seems to be missing. Is the code for that done? Make sure that the match can find multiple instances of the pattern in sample text.

I am struggling to visualize the save_id part, once that is clear will review the rest.