refactor: `RegistryBuilder` duplicates six `DimensionRegistry` accessors

[shunichironomura]

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Summary

RegistryBuilder holds the same three fields that DimensionRegistry holds, and re-implements six accessors over them with identical bodies.

Detail

crates/graphcal-compiler/src/registry/types.rs:92-96 holds them as three loose fields:

pub struct RegistryBuilder {
    base_dim_names: BTreeMap<BaseDimId, String>,
    base_dim_symbols: BTreeMap<BaseDimId, String>,
    ...
    dimensions: HashMap<DimName, Dimension>,
    ...
}

and build() (types.rs:125-129) moves them verbatim into the registry:

dimensions: DimensionRegistry {
    base_dim_names: self.base_dim_names,
    base_dim_symbols: self.base_dim_symbols,
    dimensions: self.dimensions,
},

Both types then expose the same six accessors with identical bodies:

Method	types.rs	dimension_registry.rs
base_dim_names	424	169
base_dim_symbols	429	175
format_dimension	437	187
resolve_dim_expr	447	226 (#[cfg(test)])
resolve_dim_expr_detailed	455	233
resolve_type_expr	467	245

Note

The shared logic is already correctly factored into free *_impl functions in dimension_registry.rs (resolve_dim_expr_impl, resolve_dim_expr_detailed_impl, resolve_type_expr_impl, format_dimension_preferring_alias_after_validation). So this is purely six duplicated forwarders plus a duplicated field triple — a small, low-risk cleanup, not a logic duplication.

Suggested fix

Have RegistryBuilder own a DimensionRegistry under construction and delegate to it (or Deref to it for the read methods). build() then moves one field instead of three, and the accessors exist once.

Provenance

Found during a full-workspace code review at 6e462341a (v0.0.1-alpha.27). Baseline at that commit: cargo clippy --workspace --all-targets clean, cargo test --workspace 2926 passed / 0 failed, cargo deny check advisories ok.