correct strat mixing type toggleability check in discordBDStratTNT

[chad-klumb]

This PR corrects discordBDStratTNT to consider all free edges when checking strat mixing type toggleability. Formerly only non-discordant edges were considered, which in rare cases could lead to incorrect behavior.

A related test has been added, and the run lengths of some other tests have been reduced to keep total test runtime from increasing.

The new test requires the updates in ergm@ergm_block. There are no updates to ergm.multi, but the ergm.multi@ergm_block branch has been created to provide a version of ergm.multi with ergm@ergm_block in its remotes field (so that pak can solve the dependencies).

Once ergm@ergm_block is merged into ergm@master (see statnet/ergm#539), the ergm@ergm_block and ergm.multi@ergm_block remotes in this PR can be reverted to ergm@master and ergm.multi@master, and the ergm_block branches of ergm and ergm.multi can be deleted.

There was an unrelated CMLE test failure (also present in tergm@master), and I've increased the CMLE test tolerance in this branch to avoid that failure.