Add schema registry with auto-detection (#12)

[MALathon]

Summary

Implement a global registry for storing and retrieving site schemas, with support for automatic URL-based schema detection. This builds on #11 (SiteSchema base class).

Changes

New Files

• fetcharoo/schemas/registry.py - Registry implementation
• tests/test_schemas_registry.py - 35 comprehensive tests

Updated Files

• fetcharoo/schemas/__init__.py - Export registry functions

Registry API

from fetcharoo.schemas import (
    SiteSchema,
    register_schema,
    get_schema,
    detect_schema,
    list_schemas,
    schema,  # decorator
)

# Register a schema
my_schema = SiteSchema(
    name='my_site',
    url_pattern=r'https://mysite\.com/.*',
    sort_by='numeric'
)
register_schema(my_schema)

# Or use the decorator
@schema
class SpringerBook(SiteSchema):
    def __init__(self):
        super().__init__(
            name='springer_book',
            url_pattern=r'https?://link\.springer\.com/book/.*'
        )

# Auto-detect schema from URL
detected = detect_schema('https://link.springer.com/book/10.1007/978-3-031-41026-0')
print(detected.name)  # 'springer_book'

# List all schemas
print(list_schemas())  # ['my_site', 'springer_book']

Functions

Function	Description
register_schema(schema, overwrite=False)	Add schema to registry
unregister_schema(name)	Remove schema by name
get_schema(name)	Get schema by name
detect_schema(url)	Auto-detect schema from URL
list_schemas()	List all schema names (sorted)
get_all_schemas()	Get all schemas as dict
clear_registry()	Clear all schemas
is_registered(name)	Check if schema exists
schema_count()	Count registered schemas
@schema	Decorator to register class/instance

Test Plan

• 35 new tests for registry functionality
• All 304 tests pass (269 existing + 35 new)

Next Steps

This PR enables:

• Add built-in schemas for common sites (Springer, arXiv) #13 - Built-in schemas (Springer, arXiv)
• Integrate schema parameter into download functions #14 - API integration (schema parameter)

Closes

Closes #12

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Codecov Report

❌ Patch coverage is 99.59677% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
tests/test_schemas_registry.py	99.50%	1 Missing ⚠️

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