Fix build_join_buckets ArgumentError for non-OuterJoin Arel nodes

[waratuman]

Problem

Two related issues when filter_on uses non-standard join types:

1. build_join_buckets only handles OuterJoin in the left outer joins block

The override raises ArgumentError: "only Hash, Symbol and Array are allowed" when left_outer_joins_values contains an Arel::Nodes::Join subclass other than OuterJoin (e.g. InnerJoin). These nodes flow through select_named_joins → select_association_list, which yields anything that is not a Hash/Symbol/Array/JoinDependency to the block. The block only handled CTEJoin and OuterJoin.

2. Proc joins from filter_on not resolved in build_filter_joins (fixes #25)

When filter_on is called with a lambda as dependent_joins:

filter_on :columns, -> (filters) {
  if filters.is_a?(Array) && filters.size > 1
    # return Arel join sources
  else
    :columns
  end
} do |klass, table, key, value, rt, at|
  # filter logic
end

The Proc was pushed raw into relations in build_filter_joins, then sent to left_outer_joins! in filter!, where select_association_list cannot handle it.

Fix

query_methods_extension.rb: Broadened the elsif from Arel::Nodes::OuterJoin to Arel::Nodes::Join, matching the pattern already used in the joins_values block below.

predicate_builder_extension.rb: Added Proc handling in build_filter_joins — when js is a Proc, call it with the filter value to resolve the actual joins before classifying them as relations or custom.

Other changes

• Added tests for filter_on with Arel join nodes and Proc joins
• Updated CI matrix: dropped Rails 7.1 (EOL), bumped 8.1.1 → 8.1.2