fix(data): track combo costs and pagination limits

[kartojal]

Summary

• expose combo gross entry cost and entry fees as precision-preserving Decimal fields
• enforce the documented inclusive offset limits for trades and activity before an invalid request is sent
• document bounded start/end windows and cover sync/async pagination boundaries

Validation

• make check (lint, format, Pyright, 2,271 non-integration tests)
• relevant live Data API integration tests (5 passed)
• make build
• adversarial review: no findings

Linear: DEV-437

---

Note

Low Risk
Additive model fields and client-side pagination guards; behavior change is failing early with UserInputError instead of a rejected API call when offset limits are exceeded.

Overview
Adds gross_entry_cost_usdc and entry_fees_usdc on ComboPosition as optional Decimal fields (with parsing tests), so combo entry cost breakdown matches the Data API.

Introduces max_offset on OffsetPaginatedSpec and checks it in sync/async offset pagination before HTTP: trades cap at 10,000, activity at 5,000, raising UserInputError with guidance to narrow via start/end. Public and secure client list_trades / list_activity docstrings document those limits; unit tests assert spec limits and boundary rejection without extra requests.

^{Reviewed by Cursor Bugbot for commit 5467ac2. Bugbot is set up for automated code reviews on this repo. Configure here.}