feat(lang): float and double types with ordinary operators

`float` (32-bit) and `double` (64-bit) with + - * / %, comparisons and unary minus.
Decimal literals take their type from context and stay `fixed` elsewhere; int and long
promote implicitly (LUDIC_WARN_FLOAT_PROMOTE=1 lists every promotion). float(), double(),
int(), long() and fixed() convert; floats(n)/doubles(n) buffers; float fields, globals,
constants and parameters; Math.* computes in float for float arguments; string/print
write the shortest round-tripping decimal; float_bits/float_from_bits expose the bits.
@deterministic code may not use floats. The f_* runtime helpers stay as they are.

Editors know the new type words; the JetBrains plugin is 1.5.0.

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

docs/language/math/_section.md

@@ -5,3 +5,5 @@ order: 6
 ---
 
 Deterministic fixed-point math. Every function is computed in Q16.16 with plain integer arithmetic, so results are bit-identical on every platform and every run — the same guarantee the rest of the runtime gives. Arguments are positional.
+
+Given a <code>float</code> or <code>double</code> argument, the same functions compute in that type instead (using the platform's math library) and return it — <code>floor</code>, <code>ceil</code> and <code>round</code> included, which return an <code>int</code> only for <code>fixed</code>. <code>sign</code> returns an <code>int</code> either way. <code>trunc</code> and <code>atan</code> exist only for floats.