tx_info should be optional in TransactionContext

[tdelabro]

When doing a RPC call to a specific contract entry point, there is no transaction context, because there is no transaction, just a call. Nevertheless CallEntryPoint::execute method takes an EntryPointExecutionContext as an argument, which contains a TransactionContext which has a field of type TransactionContext.

https://github.com/eqlabs/pathfinder/blob/e4ed0d0f24803bda31dd62c072fa75d7ab5657b3/crates/executor/src/call.rs#L51

As you can see there, the lib users end up passing a default, empty TransactionContext. Pathfinder is doing it, we are doing it too in Madara.
This is a clear sign of a design flaw. Either the execute method should be changed to take two separated args block_context: BlockContext and tx_info: Option<TransactionInfo> or the tx_info fields of the TransactionContext should be changed to be optional.

It then becomes a bit weird to keep this type named TransactionContext, when it is also used for calls, which are not transactions. Maybe ExecutionContext would be better, or EntrypointExecutionContext to be more explicit.