refactor(nango): overhaul crate with connect_session.rs and connection.rs modules

[devin-ai-integration]

refactor(nango): split into connect_session.rs and connection.rs modules

Summary

Overhauls crates/nango based on the current Nango API reference. The monolithic types.rs and client.rs are split into domain-specific modules, types are renamed for clarity, and all missing API endpoints are implemented.

Structural changes:

• connect_session.rs — types + impl NangoClient for create, reconnect, get, delete sessions
• connection.rs — types + impl NangoClient for create, list, get, patch, delete connections + set/update metadata
• client.rs — slimmed to core builder, shared response helpers (check_response/parse_response), and proxy method
• types.rs — only shared types (NangoIntegration, webhook types)

Type renames: NangoConnectSessionRequest → CreateConnectSessionRequest, NangoConnectSessionRequestUser → EndUser, NangoGetConnectionResponseData → Connection, NangoConnectWebhook → ConnectWebhook, etc.

Error handling: Replaced the response-enum pattern (NangoConnectSessionResponse::Ok / ::Error) with status-code-based check_response helper. Error variant renamed NangoError(String) → Api(u16, String).

API path fix: get_connection now hits /connections/{id} (plural, matching docs) instead of the old /connection/{id} (singular), and requires provider_config_key query param.

Review & Testing Checklist for Human

• Connection.id type changed from String to i64 and credentials changed from typed NangoCredentials enum to serde_json::Value. Verify no downstream code (including any generated TypeScript bindings via specta) depends on the old shapes.
• get_connection now requires a second provider_config_key parameter and the URL path changed from /connection/ to /connections/. Confirm this matches your actual Nango environment behavior and that all call sites are updated.
• get_connect_session() / delete_connect_session() — these hit /connect/session (singular). The Nango docs suggest these endpoints may require the connect session token as bearer auth rather than the API secret key. The client always sends the API key. Verify whether these work correctly or if a token-override mechanism is needed.
• ConnectWebhook / ConnectWebhookEndUser renamed from NangoConnectWebhook / NangoConnectWebhookEndUser. Check webhook handler code isn't broken.

Suggested test plan: Call create_connect_session and list_connections against a real Nango environment to verify the new response parsing works. The existing tests are #[ignore]d and require real credentials.

Notes

• Link to Devin run: https://app.devin.ai/sessions/d3d41297e8144d138ff666a4e078f74c
• Requested by: @yujonglee

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[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 1 potential issue.

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