Add changeMarginMode method to ExchangeAdapter and Standx classes

- Introduced `changeMarginMode` method in `ExchangeAdapter` interface to allow margin mode adjustments.
- Implemented the `changeMarginMode` method in `StandxExchangeAdapter` to interact with the gateway for changing margin modes.
- Added corresponding `changeMarginMode` method in `StandxGateway` to handle API requests for margin mode changes.
- Enhanced `MakerPointsEngine` to ensure isolated margin mode before order placement, with appropriate logging and defense mode activation if the change fails.
- Created tests for margin mode functionality to validate behavior under different scenarios.

tests/maker-points-defense-rest.test.ts

@@ -99,6 +99,8 @@ describe("MakerPointsEngine defense-mode REST polling", () => {
       standxRestUnhealthy: false,
       standxRestConsecutiveErrors: 0,
       standxRestLastError: null,
+      marginModeNotIsolated: false,
+      marginMode: "isolated",
       standxDepthAge: 6000,
       binanceAge: 0,
       standxAccountAge: 0,
@@ -149,6 +151,8 @@ describe("MakerPointsEngine defense-mode REST polling", () => {
       standxRestUnhealthy: false,
       standxRestConsecutiveErrors: 0,
       standxRestLastError: null,
+      marginModeNotIsolated: false,
+      marginMode: "isolated",
       standxDepthAge: 6000,
       binanceAge: 0,
       standxAccountAge: 0,
@@ -162,4 +166,3 @@ describe("MakerPointsEngine defense-mode REST polling", () => {
     engine.stop();
   });
 });
-