Trim stracktrace on bail:meme

[dozreg-toplud]

@midden-fabler noticed that the runtime process would occasionaly get aborted if a bail:meme involved large stacktrace - it would be too big to copy out in _cm_stack_unwind, causing us to bail:meme on the home road again.

This PR adds stack trace trimming on the deepmost road if we crash with meme moat and the stacktrace happens to be bigger than 1024 frames. It stitches up the beginning and the ending parts with [%mean 'meme: trace'] which would typically get cut off by +mook anyway. Such operations on the stacktrace are safe for the nondeterministic crashes, as documented in the comment.

Note: for this to work end must be a subnoun of beg, which should be true considering the comparisons I used.

[dozreg-toplud]

And to reproduce the issue, run this in Dojo:

!:  |-($)

[dozreg-toplud]

closing in favor of #993; this particular fix wouldn't work without mug clearing / use_w assertions since the trace is injected into Arvo later