Default address in eth_call/eth_simulate/eth_estimateGas

[MarekM25]

We use 0xfffffffffffffffffffffffffffffffffffffffe for all calls by default, while all other clients (or almost all—Geth and Besu for sure) use the 0x000...000 address, which can cause differences in RPC results.
Reference: BlockchainBridge.cs#L259

However, the task is not as simple as just changing the default address. The system address is later translated into the IsSystem flag in BlockchainProcessor, so all usages of that flag must be carefully reviewed and adjusted accordingly.

I propose starting with unit tests.