Fix hex string literal (x'...') parsing in CREATE TABLE DEFAULT values

[predictor2718]

Summary

• The lexer incorrectly tokenized x'...' hex string literals as two separate tokens (keyword x + string
  '...'), producing invalid SQL x AS '...' on rebuild
• Added states 11-13 to the number parsing state machine (analogous to states 7-9 for b'...' binary literals) to
  recognize x'...' and X'...' as single hex string literal tokens
• Added FLAG_NUMBER_HEX_STRING to prevent incorrect hexdec() conversion of the token value

Fixes #649

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.93%. Comparing base (4c45eac) to head (5081e1b).

Additional details and impacted files

@@             Coverage Diff              @@
##             5.11.x     #650      +/-   ##
============================================
+ Coverage     96.92%   96.93%   +0.01%     
- Complexity     2316     2331      +15     
============================================
  Files            71       71              
  Lines          5110     5128      +18     
============================================
+ Hits           4953     4971      +18     
  Misses          157      157              

Flag	Coverage Δ
unit-7.2-ubuntu-latest	96.93% <100.00%> (+0.01%)	⬆️
unit-7.3-ubuntu-latest	96.92% <100.00%> (+0.01%)	⬆️
unit-7.4-ubuntu-latest	96.90% <100.00%> (+0.01%)	⬆️
unit-8.0-ubuntu-latest	96.92% <100.00%> (+0.01%)	⬆️
unit-8.1-ubuntu-latest	96.92% <100.00%> (+0.01%)	⬆️
unit-8.2-ubuntu-latest	96.86% <95.00%> (-0.01%)	⬇️
unit-8.3-ubuntu-latest	96.86% <95.00%> (-0.01%)	⬇️
unit-8.4-ubuntu-latest	96.86% <95.00%> (-0.01%)	⬇️
unit-8.5-ubuntu-latest	96.86% <95.00%> (-0.01%)	⬇️

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