Format() previously handled only %d, %s and %%; any float directive rendered
verbatim, and on the QBE backend a float argument failed to compile because the
double value was stored with 'storel <d-temp>', which QBE rejects.
RTL (blaise_float.pas): add _FormatFloatSpec(V, Spec, Prec) — a precision-aware
renderer for %f/%F, %e/%E and %g/%G built on the existing Grisu1 digit
generator, with round-half-up at the precision boundary (including all-nines
carry) and printf-style exponent formatting.
RTL (blaise_str.pas): rewrite _StringFormatN to parse the full
%[-][width][.prec]<conv> specifier syntax, render each argument (int/string/
float) into a growable buffer, and apply field-width space padding. A new
arg tag (2) carries the IEEE-754 binary64 bit pattern for float values.
QBE codegen: float Format arguments now emit tag 2 and reinterpret the double
bits to an integer via 'cast' before storel, fixing the compile error.
Tests: IR unit tests assert tag-2 emission and the bit cast. E2E coverage and
the native backend follow in the next commit.
7c26598bb8