Fix handling of segment groups

[nirmal070125]

Purpose

• checking the first segment to decide whether to traverse a segment group or not is not always correct.
• there are segments that are optional.
• we have to traverse through the segments of a group and find an appropriate match.

[codecov]

Codecov Report

Attention: Patch coverage is 87.87879% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70.74%. Comparing base (3b5457e) to head (8940773).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
ballerina/segment_group_reader.bal	87.87%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
- Coverage   71.18%   70.74%   -0.45%     
==========================================
  Files          11       11              
  Lines         701      728      +27     
  Branches      256      267      +11     
==========================================
+ Hits          499      515      +16     
- Misses        202      213      +11     

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