Add HEK (Heliophysics Event Knowledgebase) data source integration

[mudhoney]

Implement complete HEK event fetching, processing, and legacy API support:

Source & Validation:

• Add HEK Source with pagination support (overmax field handling)
• Validate events have kb_archivid and supported event_type
• Support 20 event types: AR, CE, CH, EF, FI, FL, SG + 13 generic types

Processors:

• EventTypeProcessor base class with timeline, label, link, views generation
• Specialized processors: AR, CE, CH, EF, FI, FL, SG with custom labels
• Coordinate time logic: peak time for FL, end time for SPoCA events
• Region ID handling with NOAA 4-to-5 digit conversion (post July 14, 2002)

Legacy API:

• HEK events use kb_archivid as legacy_id
• Add concept field from source for HEK events
• Group contact/url from frm_contact and frm_url
• Add all 20 HEK event types to path dictionary with pins