Add Hook Interface for Customizable XSD Parsing and Code Generation

[eleenmohd-wk]

PR Details

This PR introduces am optional plugin system via the Hook interface that allows users to customize the XSD parsing and code generation process without modifying xgen's core logic.

There are 5 interception points:

• OnStartElement: Intercept XML start elements during parsing
• OnEndElement: Intercept XML end elements during parsing
• OnCharData: Intercept character data/text content during parsing
• OnGenerate: Intercept code generation before each type is processed
• OnAddContent: Post-process generated code content

During XML parsing (parsing.go), the hook intercepts the XML token stream before xgen processes it. Each hook method returns a next boolean - if false, xgen skips that element, allowing custom filtering or preprocessing.

The hook intercepts code generation (genGo.go) at two points:

1. Before generating code for each type (OnGenerate): Can skip generating specific types by returning false
2. After generating each code block (OnAddContent): Receives a pointer to the generated code string. Can modify, enhance, or replace the generated code

Description

Adds Parser.Hooks map[string]Hook for handling custom logic on specific elements

Related Issue

Motivation and Context

expands functionality w/o major changes to the core code. the hook is optional and all existing code continues to work without modification so there's no changes in the existing functionality

How Has This Been Tested

unit tests

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

❌ Patch coverage is 89.23077% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.29%. Comparing base (2cb22a3) to head (4cf8ad1).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
parser.go	78.26%	3 Missing and 2 partials ⚠️
genGo.go	95.23%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
+ Coverage   81.92%   84.29%   +2.36%     
==========================================
  Files          37       37              
  Lines        1870     1636     -234     
==========================================
- Hits         1532     1379     -153     
+ Misses        246      163      -83     
- Partials       92       94       +2     

Flag	Coverage Δ
unittests	84.29% <89.23%> (+2.36%)	⬆️

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