feat: add FetchItems endpoint and missing Item model fields

[bernardoveras]

Add GET /items support via FetchItems() method with optional pagination through new ItemListParameters class. Also add missing Item fields: userAction, autoSyncDisabledAt, consentExpiresAt, products, and oauthRedirectUri.

[Gabrielpanga]

Hi @bernardoveras thanks for the pr!

Currently listing items is not available in the api, but we are in internal discussions to liberate that for users to list the connections.

[Gabrielpanga]

🤖 AI Review

Clean, well-structured PR that follows existing SDK patterns. A few observations:

Looks good:

• FetchItems follows the same pattern as FetchAccounts, FetchInvestmentTransactions, etc.
• ItemListParameters with ToQueryStrings() matches the existing parameter class pattern.
• New Item fields use appropriate types (DateTime? for nullable timestamps, IList<ProductType> for products).
• Optional parameter with null default is clean.

Minor suggestions (non-blocking):

• UserAction is typed as string. If the API returns a fixed set of values (e.g. "NEEDS_RECONNECT", "WAITING_USER_INPUT"), consider creating an enum like ItemStatus for type safety. Fine to defer if the set of values is still evolving on the API side.
• OauthRedirectUri could arguably be Uri instead of string, but string is consistent with how other URI fields are likely handled in the SDK, so this is fine.

No issues found. LGTM.