Feat/dev engine

[koenvo]

Add debug_source() helper for easy source development

Adds a new debug_source() function that simplifies testing and debugging sources during development.

Key features:

• Single function call to test any source with minimal setup
• Automatic ephemeral storage in /tmp (or persistent if needed)
• Auto-configures logging
• Returns engine for further inspection
• Works with both simple sources and those using discover_selectors()

Example usage:

from ingestify import debug_source

source = MySource(name="test", ...)
engine = debug_source(
    source,
    dataset_type="match",
    data_spec_versions={"match": "v1"}
)

Also includes:

• engine.run() alias for engine.load() (more intuitive)
• Optional dev_dir parameter for custom storage location
• Updated README with development workflow guide

Replaces boilerplate setup code in every source file with a single helper function.