feat(core): simulate realistic network conditions

[AvhiMaz]

Closes #529

• Add --transaction-drop-rate <0.0-1.0> flag: randomly drops transactions with the given probability, simulating
  packet loss or leader rejection
• Add --transaction-execution-delay-ms <ms> flag: applies a random delay (0 to N ms) before executing each
  transaction, simulating out-of-order processing under high throughput
• Add TransactionStatusEvent::Dropped variant returned to the RPC client when a transaction is dropped

Usage:

surfpool start --transaction-drop-rate 0.1 --transaction-execution-delay-ms 200

[AvhiMaz]

the ci failure in test_time_travel_absolute_timestamp appears to be a pre-existing flaky test unrelated to this mr.

can you review this, @MicaiahReid @lgalabru ? thanks :)