Determine right value for initial memory pages

[raulk]

Context

For M1 (nv16), we are going with unlimited max pages given that the system can only run trusted logic via builtin system actors. However, it's not clear what the value of initial pages should be, in order to avoid excessive memory expansion operations.

Request

• Run test vectors tracing memory expansions.
• Analyze the traces and determine the right value for initial pages.
• Get a sense of average and maximum memory usage.
• Feed this info into #341.