feat: update Entity flag field types to bool (Tango #2377)

[infinityplusone]

Companion to Tango #2377 (serializer + shaping parity for retyped Entity fields).

Tango's 0064_lakehouse_consumer_cleanup booleanizes nine Entity flag fields and drops source_type. After it ships, /api/entities/ and webhook alerts.entity.match payloads serialize those flags as JSON true / false / null instead of the legacy string tokens. tango-python should update its Entity Pydantic model to match.

Field type changes (str → bool)

Field	Old (str tokens)	New (bool)
registered	"Y"	true
registration_status	"Active" / "Inactive"	true / false
uei_status	"Active" / "Not Active"	true / false
public_display_flag	"Y" / "NPDY"	true / false
bonding_flag	"YES" / "NO"	true / false
disaster_registry_flag	"YES" / "NO"	true / false
debt_subject_to_offset	"Y" / "N"	true / false
credit_card_usage	"Y" / "N"	true / false
edi_information_flag	"Y" / "N"	true / false

All nine should be Optional[bool] — pre-0064 tokens outside the known set (or NULL) map to None. The NPDY → false mapping for public_display_flag is the one non-obvious one; literal interpretation is "Not Publicly DisplaYed".

Other changes from the same migration

• source_type: removed entirely from the API response. Remove it from the Pydantic model. Consumers that read entity.source_type should switch to entity.source (already populated, same semantic).
• Seven *_desc top-level fields (purpose_of_registration_desc, entity_structure_desc, entity_type_desc, profit_structure_desc, organization_structure_desc, state_of_incorporation_desc, country_of_incorporation_desc) are removed from the default entity payload. They were already accessible via ?shape=…(*) expansion, which now derives {code, description} at render time and is unchanged in shape. If the SDK's Entity model has any of those top-level keys, drop them.
• evs_source and exclusion_status_flag are now strictly enforced enums on the server ({"D&B", "E&Y"} and {"Y", "N", "D"} respectively). They still come back as strings; no SDK type change needed beyond optionally narrowing the field to a Literal[...].

Action items

• Update Entity model field types in tango/models.py.
• Bump record cassettes if any tests assert string values on the renamed fields.
• CHANGELOG entry on the SDK side flagging the breaking change for downstream Python consumers.

~ Hal