libghidra v0.0.6

• Xrefs pushdown — exact incoming-reference, per-function reference, and bounded
  destination-function lookups, as additive ListXrefs request fields. XrefRecord
  now carries from/to function identity, so a caller building a call graph no longer
  issues one GetFunction per edge. Wire-compatible in both directions.
• ListLeafFunctions — host-native leaf listing, evaluated per candidate rather
  than rescanning the whole program on every page.
• Cancellation — out-of-band POST /cancel, scoped per client via the
  X-LibGhidra-Client header so one client cannot abort another's in-flight RPCs.
  Cancellation now reaches Ghidra's own algorithms (a real TaskMonitor, not DUMMY).
• Listing performance — comment scans use the comment-address index instead of
  walking every code unit; ListDataItems streams its range instead of accumulating
  the program per page.
• Session lifecycle — a failed save is reported (SAVE_FAILED) rather than
  silently swallowed; an absent shutdown policy stays UNSPECIFIED instead of
  becoming an implicit save; close(ShutdownPolicy) replaces the boolean, which
  could not express NONE.
• Headless — POSIX hosts are reaped when their owner dies; the platform-native
  launcher script is preferred; libghidra decompile --require-exact rejects
  fallback output.

Full changelog: v0.0.5...v0.0.6