Apply table/schema filters when fetching FK constraints

[teknogeek0]

Summary

• schema_list_fk_constraints accepted a SourceFilters * parameter but never used it, causing all FK constraints to be fetched regardless of --exclude-table or --exclude-schema filters
• When pgcopydb reached the post-restore FK constraint creation step, it would attempt constraints where the referencing or referenced table didn't exist on the target, causing a hard failure
• No data is affected — only the final ALTER TABLE ... ADD CONSTRAINT ... FOREIGN KEY step failed

Changes

• Added listSourceFKConstraintsSQL[] with filter-aware SQL variants following the same pattern as listSourceIndexesSQL
• The EXCL variant left-joins both the referencing table and the referenced table against filter_exclude_schema and filter_exclude_table, skipping constraints where either side is excluded
• The INCL variant inner-joins both tables against filter_include_only_table
• prepareFilters is already idempotent (filters->prepared guard), so calling it from both schema_list_all_indexes and schema_list_fk_constraints in the same session is safe

Test plan

• Added foo.tbl_ref_target (excluded by table filter) and foo.tbl_with_fk_to_excluded_tbl (FK referencing the excluded table) to the filtering test fixture
• New test 5-fk-constraints.sql verifies both the excluded-schema and excluded-table FK scenarios result in count 0 on the target
• Full test suite (DOCKER=podman PGVERSION=16 make tests) passes