stillwater-sc / universal / 30333181328

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feat(integer): add fma(a,b,c) (#1231)

* feat(integer): add fma(a,b,c)

integer had no fma. Add a free sw::universal::fma(a,b,c) = a*b + c so generic ADL
code (dot products, polynomial evaluation) compiles and runs over integer.

Integer arithmetic is exact, so there is no fused-vs-two-rounding distinction; and
because fixed-size integer arithmetic is modular, wrapping the product before adding
c yields the same value as wrapping once at the end -- (a*b + c) mod 2^nbits --
consistent with integer's own operator* / operator+.

Test (static/integer/binary/math/fma.cpp) validates against an independent int64
modular oracle (exact a*b + c wrapped to nbits): exhaustive (a,b) for integer<8>,
randomized checks up to integer<32>, agreement with the operator form a*b + c,
identities (fma(a,b,0)==a*b, fma(0,b,c)==c, fma(1,b,c)==b+c), and the maxpos^2+maxpos
modular-overflow corner. Oracle uses int64 (not __int128, which MSVC lacks), guarded
by static_assert(nbits <= 32). Green on gcc + clang.

Resolves #1192
Relates to #1189

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* style(integer): wrap fma test registrations to the 120-column limit

CodeRabbit: the ReportTestResult registration lines exceeded the project's
.clang-format ColumnLimit of 120 (136-140 cols). Break each onto two lines.
No behavior change; still green on gcc + clang.

Relates to #1192

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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