Implement Integer and String eql?/equal?

[ryanseys]

Integer and String eql?/equal? on typed receivers returned false even for
equal values, because no codegen handler existed and they fell through to the
unsupported-equality path. == already worked, and Float#eql? was already
handled — this mirrors that shape in the Integer and String arms of the
typed-receiver method dispatch (emit_scalar_call).

• Integer#eql?/equal?(x): value-equal only when x is itself Integer-typed.
  No numeric coercion, so 1.eql?(1.0) is false. equal? on a fixnum is value
  identity, identical to eql? here. A Float or other concrete arg is never
  equal; a polymorphic arg checks its runtime tag.
• String#eql?(x): byte-equal (via the existing sp_str_eq) only when x is
  String-typed, with no coercion.
• String#equal?(x): object identity. Strings are const char * whose literals
  the C compiler merges at -O2, so raw pointer equality would wrongly equate
  distinct equal-valued literals (a = "x"; b = "x"; a.equal?(b)). Instead the
  reflexive case is resolved syntactically: equal? is true only when the
  receiver and argument are the same side-effect-free lvalue (the same local or
  instance variable read, e.g. x.equal?(x)); every other form is
  conservatively false. This faithfully models x.equal?(x) without the
  merged-literal false positives. The one gap is aliasing through assignment
  (a = s; a.equal?(s)), which reads as false.

The general poly-receiver eql?/equal? dispatch is left for a follow-up, as
it needs the runtime value-equality helper in lib/sp_runtime.h.

New test test/eql_equal.rb (expected regenerated from ruby) covers
Integer/String eql?/equal?, the 1.eql?(1.0) false case, String equal?
identity (same var true; distinct equal-valued and distinct literals false), and
a typed receiver with a polymorphic argument. make test is green (1032 pass,
0 fail, 0 error).

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

[gemini-code-assist]

Code Review

This pull request adds support for the eql? method on typed String and Integer receivers, as well as the equal? method on typed Integer receivers. The implementation handles both concrete and polymorphic arguments and includes corresponding test cases. Feedback on the changes suggests also implementing String#equal? using pointer equality, as the current implementation does not handle object identity for strings, which would incorrectly return false even when comparing a string variable to itself.

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