Change volume data type in MarketCandle

[BZ-CO]

Change volume data type in MarketCandle from double to decimal.

[vslee]

@BZ-CO, I will be pushing out a new NuGet soon. Before I do so, can you take a look at the test:

MEXCAPITests.GetTickersAsyncShouldReturnTickers()

Looks like it's failing because the volume of DTUSDT is 136651248485429227479402823307.68, which overflows decimal. Now we didn't even have MEXC support until you added it, so I'm going to defer to you on this one. Would you like to keep this change to decimal (which I'm fine with), or rollback?

{{ "symbol": "DTUSDT", "priceChange": "-0.000000000000000000000001", "priceChangePercent": "-0.25", "prevClosePrice": "0.000000000000000000000004", "lastPrice": "0.000000000000000000000003", "bidPrice": "0.000000000000000000000002", "bidQty": "674761418857801392904627655.1", "askPrice": "0.000000000000000000000003", "askQty": "218152129484027038417612334.96", "openPrice": "0.000000000000000000000004", "highPrice": "0.000000000000000000000019", "lowPrice": "0.000000000000000000000002", "volume": "136651248485429227479402823307.68", "quoteVolume": "557005.162690709267440406353736", "openTime": 1731956703065, "closeTime": 1731956770502, "count": null }}

[BZ-CO]

@vslee, I've tested the other exchanges, and everything seems ok there. There are only a few pairs with such high volume on MEXC and we will just exclude them. Will send a fix now.