Fix five categories of optimizer reconstruction bugs

1. Type inference: When egglog rewrites change operation domain (e.g.,
   Select→IAdd), the reconstruction now infers correct SPIR-V types
   instead of blindly using the original instruction's type. Adds
   TypeClass classification and infer_result_type for both top-level
   instructions and nested materialize_term sub-expressions.

2. Binding order: Egglog let-bindings are now emitted in topological
   dependency order instead of sorted by numeric ID. This prevents
   "unbound symbol" crashes when block processing order puts a higher
   ID into id_to_term before a lower ID that references it.

3. Duplicate IDs: Synthesized constants and folded constants are now
   deduplicated before adding to types_global_values, preventing
   "id defined more than once" errors.

4. Dominance: Synthesized intermediate instructions are now placed in
   the same block as the root instruction they serve, instead of always
   in block 0 of function 0. This prevents dominance violations when
   operands are defined in different blocks.

5. Loop preservation: Selection constructs inside loop bodies are now
   skipped for RVSDG EffGamma transforms, preventing block terminator
   rewrites from breaking continue-block reachability.

Author: LegNeato