v0.3.1

• Parser warnings: PSS/E and PowerWorld .aux parse warnings now surface
  through Parsed::warnings and the C ABI's pio_warnings path instead of
  living only in docs or writer warnings.
• PSS/E: hardened record tokenization and continuation handling. Slash
  characters inside quoted fields are no longer treated as comments; incomplete
  transformer and two-terminal DC continuation records now error clearly instead
  of consuming section terminators; transformer records with non-unit CW/CZ
  now warn that impedance and turns values were read without conversion.
• PSS/E: load ZIP components and v34/v35 load tail fields are retained in extras
  and replayed on write. If typed load p/q no longer match retained
  PL/QL/IP/IQ/YP/YQ, the writer emits typed constant power and reports the
  stale extras instead of replaying wrong source components.
• PSS/E: quoted IDs, names, and HVDC names are sanitized before duplicate ID
  allocation, so collisions created by replacing quotes or / are handled
  deterministically and reported in conversion warnings.
• Normalization: generator cost per-unit scaling now dispatches through explicit
  cost models, and slack bus selection ignores NaN generator pmax values
  when choosing among candidate reference buses.
• PSLF and PowerWorld AUX tokenization: quoted / and // text is kept as data
  rather than treated as continuation or comments. PowerWorld .aux now reports
  unmodeled DATA blocks as parse warnings while retaining source text for
  same-format writeback.
• powerio-dist OpenDSS: quoted comment markers are preserved in lexer values,
  indented block comments are skipped, capacitor and reactor kvar shunts share
  validation, reactors with kvar/kv map to typed shunts with negative
  susceptance, and invalid shunt forms stay untyped with explicit warnings.
• powerio-dist BMOPF: fixed OpenDSS generators with fixed P/Q setpoints now
  encode as negative BMOPF loads with warnings. The vendored draft schema was
  refreshed for multi-digit matrix keys, corrected $id, and nonnegative
  switch i_max, so 10-conductor linecode output validates without the old
  schema warning.
• C distribution ABI v1 (PIO_DIST_ABI_VERSION 1): direct pio_dist_* callers
  get a separate version check; the supported one-shot conversion order is
  (input, from, to, ...).
• C ABI tests now reject the old target-before-source conversion order for both
  pio_convert_* and pio_dist_convert_*, including the compiled C smoke test
  against powerio.h.
• C ABI hardening: unit tests pin every public PIO_* macro, opaque typedef,
  and pio_* prototype in powerio.h; Cargo now checks Rust source/header
  symbol parity; CI builds the no-default core ABI plus the release
  arrow,gridfm,dist feature smoke test and C++ header/link sanity checks.
• No core C ABI break; PIO_ABI_VERSION stays 4. No existing Rust or Python
  API was removed or reordered.

What's Changed

• [codex] Harden parser tokenization and dist shunts by @samtalki in #138

Full Changelog: v0.3.0...v0.3.1