fix: reject non-finite provider prices, and read them as unpriced

A nan or inf in [providers.*] survived float() and reached the cost
arithmetic, rendering $nan or, for -inf, a negative cost. Worse than a
display wart: is_priced answered True, so the readout took the priced
branch and showed a poisoned figure in the one state the ? is there to
admit it cannot say.

Guarded at both ends. providers._number mirrors models._get, which
already covered the models.ini writer. is_priced states its own
predicate completely rather than trusting its callers, since the dialog
is a third writer and the file is documented for hand-editing.

Records why float money stays, and that exact-equality assertions in the
cost test hold for the chosen prices rather than in general.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions