Bugfix: do not build nocase filters for non-String types

[dimitrovmaksim]

Resolves #6239

Fixes incorrect generation and execution of case-insensitive list filters (_contains_nocase, _not_contains_nocase) for non-String types, resulting in SQL error operator does not exist: bytea ~~* bytea

1. Schema Generation (graph/src/schema/api.rs)

• Only emit _nocase list filter variants when the element type supports case-insensitive operations
• Updated test validates that pools: [Pool!]! (Bytes ID) no longer generates nocase filters

2. Query Execution (store/postgres/src/relational_queries.rs)

• Added validation to reject ILike/NotILike operations on non-String columns
• Returns clear UnsupportedFilter error instead of opaque SQL failure

Note: I don't think there's a way to do this without returning any kind of error, unless we silently downgrade nocase to casesensitive for non-String types, or cast other types to ::text in the where clause.