machxo3: timing fuzzers

[Ravenslofty]

Timings that are presently missing:

• block RAM (possibly due to the NES core using too much block RAM and Diamond blowing memory to DFFRAM?) due to SDF issues
• I/O delays (despite running the I/O delay fuzzer, it doesn't seem to pick up any timings?)
• interconnect delays (TODO)

[mmicko]

This is already part of https://github.com/YosysHQ/prjtrellis/pull/234