Add contingent orders support: order groups and order sends order

[Martin-Molinero]

Description

Places contingent order sets through TradeStation's native order relationships:

• OCO/BRK order groups through the order groups endpoint. BRK maps the one updates other contingency.
• Orders triggered by another are sent as OSOs of their parent, grouped when they are related to each other.
• Held children are reported as triggered once their parent fills.
• The contingencies of open orders are rebuilt from their linked orders (OCO, BRK, OSO and OSP relationships) through OrderContingency.Trigger/Relate.
• TradeStation confirms the orders sent by another (OSO) before it: the placed orders are matched in that order, ruling out a confirmation for another side or order type.
• Orders TradeStation cancels itself (CAN), like the orders sent by a canceled order, are reported as canceled.
• The sent but not yet acknowledged orders (OPN) are loaded as open orders, they were skipped.
• TradeStation cancels the rest of a group when a member fills, not when one is canceled: canceling a member warns once that the rest keep working.

Related Issue

Requires QuantConnect/Lean#9828, which adds contingent orders to Lean. This PR builds against it, so CI will pass once it's merged and released.

Motivation and Context

Support for Lean contingent orders (OCO, OTO, OUO, brackets) using the brokerage's native functionality, so the sets are placed atomically and managed on the brokerage side.

Requires Documentation Change

The supported contingent order shapes of this brokerage, see its brokerage model in Lean.

How Has This Been Tested?

• Unit tests of the contingent orders support: request building and open orders rebuilding.
• Live on the TradeStation simulator, through the Lean BrokerageTests contingent orders suite (TradeStationBrokerageTests.ContingentOrders.cs):

Case	Equity (AAPL)	Option (AAPL)	Index option (SPXW)	Future (MES)
OCO resting: cancel one	✅	✅	✅	✅
OUO (BRK, limit + stop) resting: cancel one	✅	✅	✅	✅
OTO resting: cancel the parent cancels the held child	✅	✅	✅	✅
Bracket resting: cancel the entry cancels the held exits	✅	✅	✅	✅
OCO / OUO / OTO / bracket: every order updated, held ones included	✅	✅	✅	✅
OTO / bracket with a market parent: parent fills, children released	✅	✅	✅	✅
OCO / OUO / OTO / bracket: open orders rebuilt with the same contingencies, held ones held	✅	✅	✅	✅

• OCO with a market member: the fill cancels the other member and it's reported as canceled.
• Existing order tests, equities: market, limit, stop market and stop limit orders long/short from zero and closing (16), limit order update, update of a canceled order. CancelOrders fails as on master: the second cancel of the closed order returns true (_cancelOrderSoftRejects).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>

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