fix(span_table_functions): explicit unique_ptr<BinsBindData> -> unique_ptr<FunctionData> in Copy()

[estebanzimanyi]

GCC + DuckDB 1.4.4's unique_ptr does not implicitly convert derived to base, so return r; in BinsBindData::Copy() fails to compile:

src/temporal/span_table_functions.cpp:47:16: error: could not convert 'r'
  from 'unique_ptr<duckdb::{anonymous}::BinsBindData,...>'
  to 'unique_ptr<duckdb::FunctionData,...>'

This is a pre-existing main-branch issue that fires on a clean local build with the current vcpkg-pinned DuckDB 1.4.4. It was masked in earlier DuckDB versions which allowed the implicit derived-to-base unique_ptr conversion.

Fix

Use DuckDB's unique_ptr_cast<SRC, TGT> helper (defined in duckdb/src/include/duckdb/common/helper.hpp:130) to do the conversion explicitly:

-        return r;
+        return unique_ptr_cast<BinsBindData, FunctionData>(std::move(r));

Matches the canonical DuckDB-core pattern (see e.g. duckdb/src/include/duckdb/function/table/table_scan.hpp's TableScanBindData::Copy() which does return std::move(bind_data); for the same shape).

No behaviour change

The move is exactly what the implicit conversion would have done if the compiler accepted it. The unique_ptr_cast helper is a transparent reinterpret + ownership-transfer.

Verification

Surfaced by a fresh local build (GEN=ninja make release on a clean checkout of main + vcpkg's MEOS + DuckDB v1.4.4 submodule). After this fix, the build proceeds past span_table_functions.cpp.