Add tax lot endpoints and order_sell_tax_lot (closes #1631)

[DhruvaBansal00]

Summary

Closes #1631 by adding Robinhood tax-lot support: three read endpoints and the
sell-by-lot order variant.

New functions (exposed via robin_stocks.robinhood)

• get_tax_lots(symbol, account_number=None, info=None) — open tax lots for a stock
• get_selected_tax_lots(order_id, account_number=None, info=None) — lots tagged for a sell-by-lot order
• get_closed_tax_lots(order_id, account_number=None, info=None) — settled lots from a sell order
• order_sell_tax_lot(symbol, lots, account_number=None, timeInForce='gfd', extendedHours=False, jsonify=True, market_hours='regular_hours') — market sell that closes specific lots; lots is a list of {'open_lot_id': ..., 'quantity': ...} dicts

Endpoints wrapped

Method	Path
GET	/tax_lots/open/{account_number}/{instrument_id}/
GET	/tax_lots/order/{order_id}/selected/
GET	/tax_lots/order/{order_id}/closed/
POST	/orders/ with tax_lot_selection_type: "custom" + tax_lots: [...] + position_effect: "close"

The sell-by-lot order uses the same /orders/ endpoint as order(), just with three extra payload fields. Posted as JSON (the existing order() uses form-encoding, but the nested tax_lots list needs JSON).

Conventions followed

The three read functions are pure pass-through using request_get(url, 'pagination', payload) + filter_data, matching get_open_stock_positions, get_dividends, etc. No data enrichment, no cross-instrument helpers.

get_tax_lots rounds the price query param via round_price() — Robinhood rejects 6-decimal precision (raw get_latest_price output) with HTTP 400, so the rounding is necessary.

Tests

TestTaxLots in tests/test_robinhood.py:

• test_get_tax_lots_for_held_position — picks a held symbol from get_open_stock_positions() and asserts the full lot schema (all 14 keys documented in the docstring)
• test_get_tax_lots_unknown_symbol — fake ticker → [None]
• test_get_selected_tax_lots_returns_list — smoke
• test_get_closed_tax_lots_returns_list — smoke

No tests for order_sell_tax_lot per the contributing guide's no-real-orders rule.

Verified against a live account

End-to-end: read paths returned correct schemas and paginated cleanly across many pages; order_sell_tax_lot placed a sell that Robinhood queued with tax_lot_selection_type: "custom" echoed back in the response.

Contributing checklist

• Only new code with new docstrings — no grammar/doc-only changes, so a single code commit is appropriate
• __init__.py updated to import new functions
• setup.py version bumped 3.4.0 → 3.5.0 (feature; YY incremented, ZZ zeroed)
• Tests added for new read functions