Rig

Switch to [SpiNNaker tools v3.1.0](https://github.com/SpiNNakerManchester/spinnaker_tools/releases/tag/v3.1.0).

The reason behind a failing SDRAM allocation is now reported by `SpiNNakerMemoryError`.

Fixes a bug which prevent the argument `boot_delay` from being used to
set the boot delay variable in the SC&MP SV struct. This is fixed by
allowing overrides to the SV struct to be provided explicitly.

For example, the call:

python
mc.boot(boot_delay=10)


Did not set the boot delay in the SV struct, whereas the new command:

python
mc.boot(sv_overrides={"boot_delay": 10})


Works as expected.

This release includes a bug fix for performing application loads which would occasionally prove unable to load applications to some regions of SpiNNaker machines.