GeezerVison

docs: abi3/Windows wheels, bundled-engine identification; release 2.4.0

Release v2.3.5: update necpp_src for Sommerfeld interpolation fix

Updates the necpp_src submodule to tmolteno/necpp@d32ed8f (master,
post PR #140):

- c_ggrid::interpolate guard restored to the NEC-2 INTRP reference
  order (already in e3f81e6): fixes wire-order-dependent impedance and
  gain over Sommerfeld ground (#139). PyNEC 2.3.4 pinned necpp_src at
  46f7fbd, which predates that fix.
- gshank Shanks-tail convergence floor restored after the issue #131
  item 3 loosening caused non-terminating rom2() integration on decks
  with wires close to a GN 2 ground.
- nec2diff fixes (#138): negative values compared, finite sign-flip
  differences, meaningful exit status.
- Regression tests: wire-order invariance unit test + testharness
  decks; nec2diff exit-code test.

Validated locally: the issue #139 reproducer (reproduce.py) passes
wire-order invariance on this pin, impedance matching the reporter's
patched reference values.

v2.3.4: Update necpp_src to v2.3.4 — impedance API changes

v2.3.2: Update necpp_src to v2.3.2

v2.2.6: Add Python 3.14 wheels, drop 3.10

v2.2.5: Fix Eigen headers missing from sdist

v2.2.4: Fix pip install from sdist (auto-generate config.h)

v2.2.3: fix wheel packaging — remove __init__.py

v2.2.2: necpp_src SC-card fix + re-enabled patch test

Version bump to 2.2.1