feat(gamma): add active filter to MarketsRequest

[skyc1e]

Summary

• Add active: Option<bool> to MarketsRequest
• Matches the existing pattern used by EventsRequest (same field, same position relative to closed)
• The Gamma backend already supports ?active= on the markets endpoint; this exposes it natively so consumers don't need client-side filtering

Changes

• src/gamma/types/request.rs: one field added to MarketsRequest
• tests/gamma.rs: active(true) added to markets_request_all_params, plus three focused tests (active=true, active=false, omitted when unset)

Builder method is auto-generated by bon::Builder. Serialization handled by existing #[skip_serializing_none]. No behavior change for callers that don't set active.

Closes #267

---

Note

Low Risk
Low risk: adds an optional boolean query parameter to MarketsRequest and extends serialization tests; no behavior change unless callers set active.

Overview
Adds an active: Option<bool> filter to MarketsRequest, allowing callers to send ?active=true|false when listing markets.

Updates query-string unit tests to cover active serialization (true/false) and verify it is omitted when unset, and includes active in the all-params markets request test.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.54%. Comparing base (77264a4) to head (6afff53).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #323   +/-   ##
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  Coverage   85.54%   85.54%           
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  Files          32       32           
  Lines        5167     5167           
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  Hits         4420     4420           
  Misses        747      747           

Flag	Coverage Δ
rust	85.54% <ø> (ø)

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