fix(listen/v2): restore subscript access on typed responses

[GregHolmes]

Summary

• restore read-only response["field"] access only on the seven Listen V2 response and nested-response model classes affected by the 7.7.0 retype
• preserve canonical attribute access, nested word subscripting, unknown fields, wire aliases, and KeyError for omitted fields
• leave all unrelated generated models unchanged
• freeze the hand-written compatibility base and seven generated response classes for future regens

Why

SDK 7.7.0 removed the typing.Any member from V2SocketClientResponse, correctly restoring typed Listen V2 responses. Through 7.6, that member caused every Listen V2 response to be returned as a raw dictionary, so callers using response["field"] broke when upgrading.

This surfaced while reviewing deepgram-docs#1130. The docs should continue teaching typed attribute access; this narrow shim protects the previously working subscript syntax.

Both styles now work:

message.words[0].confidence
message["words"][0]["confidence"]
message.words[0]["confidence"]

This PR intentionally does not turn Pydantic models into full dictionaries or Mapping objects. It restores only the subscript access that triggered the customer-facing regression. Models remain immutable and attribute access remains canonical.

Verification

• pytest: 985 passed, 1 skipped
• mypy src/: clean
• mypy tests/typecheck: clean
• ruff check src/deepgram tests/custom/test_model_dict_compat.py: clean
• targeted compatibility tests pass with Pydantic 1.10.18 and Pydantic 2.x
• sync and async receive paths, all Listen V2 response variants, nested response objects, unknown fields, omitted declared fields, and unrelated-model isolation are covered
• standalone probe passes on this branch and fails on main with TypeError: ListenV2TurnInfo object is not subscriptable

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
src.deepgram	96%	92%	0	✔
src.deepgram.agent	100%	100%	0	✔
src.deepgram.agent.v1	98%	100%	0	✔
src.deepgram.agent.v1.settings	100%	100%	0	✔
src.deepgram.agent.v1.settings.think	100%	100%	0	✔
src.deepgram.agent.v1.settings.think.models	97%	100%	0	✔
src.deepgram.auth	100%	100%	0	✔
src.deepgram.auth.v1	100%	100%	0	✔
src.deepgram.auth.v1.tokens	97%	100%	0	✔
src.deepgram.core	88%	81%	0	➖
src.deepgram.errors	100%	100%	0	✔
src.deepgram.helpers	100%	95%	0	✔
src.deepgram.listen	100%	100%	0	✔
src.deepgram.listen.v1	98%	93%	0	✔
src.deepgram.listen.v1.media	97%	100%	0	✔
src.deepgram.listen.v2	98%	92%	0	✔
src.deepgram.manage	100%	100%	0	✔
src.deepgram.manage.v1	100%	100%	0	✔
src.deepgram.manage.v1.models	96%	100%	0	✔
src.deepgram.manage.v1.projects	97%	100%	0	✔
src.deepgram.manage.v1.projects.billing	100%	100%	0	✔
src.deepgram.manage.v1.projects.billing.balances	96%	100%	0	✔
src.deepgram.manage.v1.projects.billing.breakdown	97%	100%	0	✔
src.deepgram.manage.v1.projects.billing.fields	97%	100%	0	✔
src.deepgram.manage.v1.projects.billing.purchases	97%	100%	0	✔
src.deepgram.manage.v1.projects.keys	96%	100%	0	✔
src.deepgram.manage.v1.projects.members	97%	100%	0	✔
src.deepgram.manage.v1.projects.members.invites	96%	100%	0	✔
src.deepgram.manage.v1.projects.members.scopes	96%	100%	0	✔
src.deepgram.manage.v1.projects.models	96%	100%	0	✔
src.deepgram.manage.v1.projects.usage	98%	100%	0	✔
src.deepgram.manage.v1.projects.usage.breakdown	97%	100%	0	✔
src.deepgram.manage.v1.projects.usage.fields	97%	100%	0	✔
src.deepgram.read	100%	100%	0	✔
src.deepgram.read.v1	100%	100%	0	✔
src.deepgram.read.v1.text	98%	100%	0	✔
src.deepgram.self_hosted	100%	100%	0	✔
src.deepgram.self_hosted.v1	100%	100%	0	✔
src.deepgram.self_hosted.v1.distribution_credentials	96%	100%	0	✔
src.deepgram.speak	100%	100%	0	✔
src.deepgram.speak.v1	98%	97%	0	✔
src.deepgram.speak.v1.audio	91%	80%	0	✔
src.deepgram.speak.v2	98%	93%	0	✔
src.deepgram.speak.v2.audio	100%	100%	0	✔
src.deepgram.voice_agent	100%	100%	0	✔
src.deepgram.voice_agent.configurations	95%	100%	0	✔
src.deepgram.voice_agent.variables	95%	100%	0	✔
Summary	95% (6478 / 6793)	91% (1410 / 1544)	0	✔

Scope: hand-maintained SDK logic. Fern-generated data models (types/, requests/), package __init__.py files, version.py, and the unused core/http_sse/ scaffolding are excluded — see .coveragerc. Unscoped whole-package coverage is ~70%.

[dg-edcharbeneau]

Greg's fix addresses the removes the TypeError. #1130 should now be closed, not merged

[deepgram-kiley]

Approving based on @dg-edcharbeneau's previous review.