For very large blocks this prevents us from having to pause tx admission longer than necessary.

For a 100MB block it saves roughly 4 seconds from post block processing.

• use references instead of copying the hash values all the time

This MR organizes the script flags code in preparation for new features by consolidating where MANDATORY and STANDARD features are defined. It then creates a new script flag that, when active, relaxes the script stack width restriction of 520 bytes. It adds tests for large stack widths and an activation test (that can be extended for many script-related upgrade features).

This MR therefore allows the total RAM used in script stacks to increase in an unconstrained manner -- its not a viable upgrade on its own. Another MR will be created that limits the total size of the script stack.

Since this functionality is "off" until a currently-unscheduled hard fork upgrade occurs, it is fine to implement and merge these two features (relaxing the stack width limitation, and adding a total size limitation) separately.

clang-format 15.0.X is not available anymore via brew on macOS, so I tested the current available version (17.0.6) and I did not find any difference between the 2 in terms of formatting layout on the nexa code base.

Furthermore a duplicated settings (AlignTrailingComments: false) has been removed from clang-format configuration file.

Mostly I just had to add FreeBSD to the list of supported operating systems in various places. In one place I had to change the path to find the path of the executable because it's different in FreeBSD.

Unfortunately in FreeBSD the only easy way (see https://stackoverflow.com/a/1024937/428740) to get this information programtically requires configuring procfs which I have documented. I searched the code and it's only used in one place if you use rostrum.

(this is a port from BCHU)

Even thou using bitwise operator will yield the correct result, it is more readable to use boolean operators when dealing with boolean variables.