go: lex.sx — hex/octal/binary integer literals + underscores, +14 tests [consumes-lex]

Adds prefixed integer forms per Go spec § Integer literals:
0x.. / 0X.. (hex), 0b.. / 0B.. (binary), 0o.. / 0O.. (octal),
legacy 0123 octal also accepted. Underscores allowed between digits
in any run; lexer is permissive (parser/types phase can enforce
strict placement).

Dispatch lives in gl-read-number! against the first 1-2 chars;
hex digit run consumes lex-hex-digit? from lib/guest/lex.sx. Octal
and binary use local gl-oct-digit?/gl-bin-digit? — narrow enough
that promoting them to the kit is premature.

lex 92/92.

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

plans/go-on-sx.md

@@ -143,9 +143,10 @@ Progress-log line → push `origin/loops/go`.
       ident/int/string/rune/{break,continue,fallthrough,return}/{++,--,),],}}.
 - [ ] Float / imaginary literals
 - [ ] Raw string literals `` `...` ``
-- [ ] Hex/octal/binary integer literals (0x… 0o… 0b…) + underscores
+- [x] Hex/octal/binary integer literals (0x… 0o… 0b…) + underscores
+      (legacy 0123 octal also accepted; consumes lex-hex-digit?)
 - [ ] Full operator set audit (47 distinct per Go spec)
-- **Acceptance:** lex/ suite at 50+ tests. Current: 78/78.
+- **Acceptance:** lex/ suite at 50+ tests. Current: 92/92.
 
 ### Phase 2 — Parser (`lib/go/parse.sx`) ⬜
 - Consume `lib/guest/core/pratt.sx` + `lib/guest/core/ast.sx`. Chisel notes
@@ -404,6 +405,10 @@ _(none yet)_
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — Phase 1 cont.: prefixed integer literals (`0x..`, `0X..`,
+  `0b..`, `0B..`, `0o..`, `0O..`, legacy `0123`) + underscore separators
+  in any digit run. Dispatch in `gl-read-number!`; consumes
+  `lex-hex-digit?` from the kit. +14 tests, lex 92/92. `[consumes-lex]`.
 - 2026-05-26 — Phase 1 first slice: `lib/go/lex.sx` tokenizer consuming
   `lib/guest/lex.sx` predicates. 25 keywords, ident/int/string/rune lits,
   line+block comments, common operators, automatic semicolon insertion per