Add 'data pkg cleanup' to delete records from a CMT package

[zekelinAlex]

Closes #122.
Adds txc data pkg cleanup <path>. Point it at the same CMT package you
imported and it deletes those records back out of the environment.
How it works:

• parses data.xml + data_schema.xml (folder or .zip, same shapes import accepts)
• walks entities in reverse <entityImportOrder> so children come down before parents
• disassociates <m2mrelationship> pairs first so endpoints can be deleted cleanly
• batches DeleteRequest through ExecuteMultiple; on ObjectDoesNotExist, falls back to QueryExpression against the schema's primarynamefield plus every updateCompare="true" field
• shards entities across N parallel ServiceClients when --connection-count > 1
  Flags mirror import where they make sense, plus --dry-run,
  --missing-action, and the usual --yes since it's destructive.
  Also noticed data pkg convert was never wired into the command tree, so
  it was unreachable from the CLI. One-line fix in the same file.
  Tests cover the parser (folder + zip + m2m), command input validation,
  and a help-text smoke test.