Update to Substrait v0.91.0

[nielspardon]

Release notes

0.91.0 (2026-05-17)

⚠ BREAKING CHANGES

• extensions: changes the return type of the subtract:date_iday
  function from date to precision_timestamp

Features

• clarify post_join_filter. add residual_expressions to hash join and merge join (#1044) (f7b939c), closes #807
• docs: clarify distinction between enumeration arguments and options (#1005) (51ff9fa)

Bug Fixes

• extensions: correct return type for subtract:date_iday operation (#1029) (26fbd04)

See https://github.com/substrait-io/substrait/releases/tag/v0.91.0

[nielspardon]

Note on remaining work after #204 (spec 0.96.0):

Most of v0.91.0 is covered — the subtract:date_iday return-type change is in the extension YAML (absorbed by the pin; never hardcoded in src/), and post_join_filter is wired into the logical join builder.

Still missing: the residual_expression field added to HashJoinRel/MergeJoinRel (#1044) is not surfaced by the ergonomic hash_join/merge_join builders — _physical_equi_join in builders/plan.py sets only left/right/keys/type/advanced_extension. It remains settable on the raw proto, so this is an ergonomic-layer gap rather than a spec-compliance issue. Keeping this open to track exposing residual_expression (and optionally post_join_filter) on the physical-join builders.