[Custom runtimes] custom layer `pgstac_hash` and `pgstac_hash_count` do not work

`pgstac_hash` returns `"relation "searches" does not exist"` maybe because it's should `pgstac.searches` instead of `searches` in https://github.com/developmentseed/eoAPI/blob/62a8f7cbaafa029a056faa5585a9fc45fbc88a27/runtime/eoapi/vector/eoapi/vector/sql/functions.sql#L63

`pgstac_hash_count ` returns `"invalid input syntax for type integer: "('-90""` 🤷

cc @bitner

Start with runtime/eoapi/vector/eoapi/vector/sql/functions.sql, especially the function around line 63, and reproduce both reported custom-layer errors against the pgstac database schema. Check how pgstac_hash resolves searches and how pgstac_hash_count parses its input; done means both functions execute without the reported relation or integer-conversion errors.

Written by the indexing model from the issue text.