stillwater-sc / universal / 30181958815

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fix(quire): NaR-state propagation + gated overflow (no-throw config) (#1228)

* fix(quire): NaR-state propagation + gated overflow (no-throw config)

The quire threw unconditionally on NaR and out-of-range operands, ignoring the
QUIRE_THROW_ARITHMETIC_EXCEPTION macro that quire.hpp already declared. A build
that opted out of arithmetic exceptions (POSIT_THROW_ARITHMETIC_EXCEPTION 0)
still aborted the moment a NaR reached the accumulator via quire_mul -- breaking
C-ABI shims, noexcept, and -fno-exceptions contexts. (#1226)

Two complementary fixes:

1. NaR state (issue fix #2). The quire gains a sticky non-finite flag (_nan). A
   NaR/Inf/NaN operand sets it instead of throwing; it propagates through further
   accumulation (no-op once set), is cleared by a fresh finite assignment, and
   surfaces back through quire_resolve as the number system's NaR/NaN. This makes
   NaR a value -- matching scalar posit -- and removes the special case rather
   than making it configurable, so NaR never throws in either configuration.
   Comparisons treat a NaR quire as unordered (IEEE-style). Also fixes a latent
   bug: the noexcept SpecificValue ctor used to throw, i.e. call std::terminate.

2. Overflow gate (issue fix #1). The operand_too_large/small_for_quire throws are
   now gated behind QUIRE_THROW_ARITHMETIC_EXCEPTION; in the opt-out build an
   out-of-range operand is skipped (leaves the running sum intact) instead of
   throwing. Each number-system umbrella (posit, cfloat, lns, fixpnt, dbns) now
   forwards its *_THROW_ARITHMETIC_EXCEPTION to QUIRE_THROW_ARITHMETIC_EXCEPTION,
   mirroring the existing BLOCKTRIPLE forwarding.

NaR is surfaced on resolve for posit (setnar), cfloat/lns/dbns (setnan); fixpnt
has no non-finite encoding and never produces a NaR operand, so it is unchanged.

Regression test numeric/quire/posit/nar_propagation.cpp: NaR propagation,
stickiness, clear-on-assign, unordered comparisons, and resolve-to-NaR.

Verified gcc + clang: new tes... (continued)

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