Gas measurements for IPC actors and primtives

[adlrocha]

filecoin-project/FIPs#535 gives a good example of how the lack of proper gas measurement tooling for FVM (at least at the time), and the implementation of new actor logic can lead to unexpected increases of gas cost for certain operations.

Before we make a first release of the actors (and even more so if we end up deploying initially IPC as system actors initially) we should make some measurements of the gas cost of each IPC operation (from spawning a subnet, to committing checkpoints and sending cross-net messages). These measurements should have to main purposes:

• Give developers a sense of the gas costs of interacting with IPC.
• Build a better intuition of how certain low-level operations and syscalls impact the costs of gas for a method. This FIP with the latest gas changes could give us a good first overview for the analysis.
• Find potential bottlenecks and inefficiencies, and make improvements to the code to minimize the gas