Add Hash#sort_by

[ryanseys]

Implements Hash#sort_by, which previously hit the unsupported-call diagnostic. It yields each |key, value| pair and returns the [key, value] pairs ordered by the block's value.

What

• emit_hash_sort_by_expr walks the entries through the shared emit_hash_block_eval binder, building a [sort_key, pair] tuple per entry.
• A new runtime sp_PolyArray_sort_by_first sorts those tuples by their comparable sort key (sp_poly_cmp on element 0) and projects out the pairs — a Schwartzian transform. GC roots cover the dup, the working array, and the result.
• Inference reports the result as a poly array.

Testing

• New test/hash_sort_by.rb covers sorting by value, by a negated value, by string length, by the key, by a key transform (k.to_s), and over a string-valued hash — through monomorphic method parameters. Expected generated from real ruby.
• Generated C is ASAN-clean.

[gemini-code-assist]

Code Review

This pull request implements support for Hash#sort_by by adding type inference, code generation, and runtime sorting helpers, along with corresponding tests. The feedback highlights two critical safety issues: first, declaring and rooting GC variables (_tup and _tpair) inside a loop in src/codegen_fold.c can lead to dangling stack pointers and GC root stack overflow; second, using standard qsort in lib/sp_runtime.h with a comparison function that can trigger Ruby method calls is unsafe due to potential longjmp exceptions and GC compaction.

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