go: lex.sx — decimal float + imaginary literals + 22 tests [consumes-lex]

Adds Go float and imaginary literal forms per Go spec § Floating-point
literals and § Imaginary literals:
  3.14   .5   1.   1e10   1.5e-3   2.0e+2   1E5    (floats)
  2i     3.14i   1e2i                              (imag)

gl-read-number! returns one of "int" / "float" / "imag"; gl-finish-number!
factors out the post-mantissa exponent + 'i' suffix logic so the int /
float / leading-dot-float paths all share it. scan! adds a .<digit>
branch ahead of the operator matcher so '.5' tokenises as float.

ASI trigger list extended to include float + imag (Go spec § Semicolons:
all literal types trigger).

Greedy-grammar pin (a single test '1.method' lexes as float ident),
since the Go spec says the '.' after a digit always belongs to the
number, never to a following identifier.

Hex floats (0x1.fp0) deferred — not commonly used.

lex 114/114.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/go/scoreboard.md

@@ -1,10 +1,10 @@
 # Go-on-SX Scoreboard
 
-**Total: 92 / 92 tests passing**
+**Total: 114 / 114 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
-| ✅ | lex | 92 | 92 |
+| ✅ | lex | 114 | 114 |
 | ⬜ | parse | 0 | 0 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |