Nailing this leak

Dependencies

• [2] TSMS6W4D Fully commented implementation of Sized nodes + massive cleanup
• [3] OTWDDJE7 Trait/type cleanup
• [4] WS4ZQM4R Debugging, tests, etc.
• [*] OP6SVMOD Resetting history

Change contents

• replacement in sanakirja-core/src/btree/cursor.rs at line 127
  [2.39382]→[2.39382:39427](∅→∅)
  − self.first_rc_len = self.len
  [2.39382]

  [2.39427]
  + self.first_rc_len = self.len + 1