feature: add NASDAQ_SC and NASDAQ_INT equity exchanges

[Romazes]

Description

Extends the equity branch of Exchanges.GetPrimaryExchange to recognise tape letters that previously fell through to Exchange.UNKNOWN or were mis-routed, adds NASDAQ_SC and NASDAQ_INT as new Exchange entries, and fixes a copy-paste typo in the Exchange.MEMX description.

Code	Maps to	Previous behaviour
S	NASDAQ_SC	UNKNOWN
T	NASDAQ_INT	NASDAQ (conflated)
V	IEX	only long-form "IEX" recognised
H	MIAX_PEARL	UNKNOWN
U	MEMX	UNKNOWN

Related PR(s)

N/A

Related Issue

N/A

Motivation and Context

Brokerage and market-data feeds emit these tape letters in primary-exchange fields, but the equity switch in GetPrimaryExchange did not cover them. S (NASDAQ Small Cap) and T (NASDAQ Intermarket) were missing or conflated with generic NASDAQ, V (IEX) required the long-form alias, and H/U fell through to UNKNOWN. The Exchange.MEMX description was also a leftover copy of the LTSE string.

Behaviour change: "T".GetPrimaryExchange(SecurityType.Equity) now returns Exchange.NASDAQ_INT instead of Exchange.NASDAQ.

Evidence for each mapping

Code	Exchange	Sources
S	NASDAQ SC (NASDAQ Small Cap, renamed "Nasdaq Capital Market" in 2006)	thinkorswim Exchange Codes (link); Nasdaq IR "NASDAQ SmallCap Market is Renamed NASDAQ Capital Market" (link)
T	NASDAQ INT (NASDAQ Intermarket)	thinkorswim (link)
V	IEX (Investors Exchange, MIC IEXG)	dxFeed (link); UTP Vendor Alert 2015-18 (link); NYSE Daily TAQ Client Spec Appendix F (doc)
H	MIAX Pearl Exchange	dxFeed (link); NYSE Daily TAQ Client Spec Appendix F (doc); Alpaca PR#57
U	Members Exchange (MEMX)	dxFeed (link); NYSE Daily TAQ Client Spec Appendix F (doc); Alpaca PR#57

Requires Documentation Change

No

How Has This Been Tested?

Extended Tests/Common/ExchangeTest.cs:

• ExchangeCorrectlyReturnedAsSingleLetter — new [TestCase] rows for NASDAQ_SC and NASDAQ_INT exercise the round-trip assertion primaryExchange.Code.GetPrimaryExchange().
• ExchangeCases — new rows asserting "S" → Exchange.NASDAQ_SC and "T" → Exchange.NASDAQ_INT through both StringExchangeCorrectlyReturnedAsSingleLetter and ExchangeAsString.

V → IEX, H → MIAX_PEARL, and U → MEMX are one-way string aliases onto existing Exchange entries (no new round-trip to assert) and are not covered by additional test cases.

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)
• 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#>-` or `feature-<issue#>-`