v0.7.4

Changed

• Minimum panproto version raised from 0.52.0 to 0.52.1.
  The release resyncs the _native.pyi stubs to the runtime
  (diff_and_classify takes a third protocol argument;
  ProtolensChain.instantiate takes (schema, protocol);
  Instance.root / node_count / arc_count are int
  properties and Instance.validate() returns the error list).
  It also tightens by-construction source emit for Rust and Julia
  (line comments no longer absorb the following items, opaque token
  trees emit verbatim, Julia parenthesised macro calls keep their
  arguments), which flows through
  didactic.codegen.source.emit_pretty and Model.emit_as.

Removed

• The two boundary casts that worked around the pre-0.52.1 stub drift
  are gone: classify_change calls panproto.diff_and_classify
  with its three runtime arguments directly, and
  DependentLens.instantiate passes the Protocol through
  without re-casting it to Schema. Behaviour is unchanged; the
  call sites now type-check against the corrected stubs.