notes
failwith instead of raise.  fix some warnings.
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checkpoint.  switching create to use a seq instead of a full icursor.  adding stuff to easily convert an icursor into a seq.
chg the main implementation of bt.Create to expect a seq of KeyValuePairs instead of tuples.  faster.
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make sure we have a test where the page manager gives no boundary
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getting rid of MemorySegment and IWrite.  this is an intermediate step.  removed or commented-out the relevant stuff in LSM fs/cs/base.  moved it all into tbase/combo.cs so that tests.cs doesn't need to change.  for now.
notes