fix(client): require 3 minute GTD expirations

[cesarenaldi]

Summary

• update GTD limit order expiration validation from 60 seconds to 3 minutes
• refresh sync and async client docstrings
• update expiration boundary tests

Verification

• uv run pytest tests/unit/test_order_limit.py
• uv run ruff check .
• uv run ruff format --check .
• uv run pyright
• uv run pytest -m "not integration"

---

Note

Medium Risk
Tightens trading input validation and may break integrations that relied on 60–179 second GTD expirations; behavior change is localized to limit orders with an explicit expiration.

Overview
Raises the minimum future expiration for GTD limit orders from 60 seconds to 3 minutes (180s) in validate_limit_order_params via _MIN_EXPIRATION_BUFFER_S.

Sync and async secure client docs for create_limit_order / place_limit_order now describe the 3-minute rule. Unit tests were updated for rejection messages and the 180s acceptance boundary.

Note: Callers passing expiration between ~60s and ~179s ahead of time.time() will now get UserInputError before sign/post.

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