fix: curio: Update pgx imports, fix db_storage alloc

[magik6k]

Related Issues

• Undo the change from fix: curio: fix incorrect null check for varchar column #11881
  • heartbeat_err is a nullable varchar, and afaict it's completely ignored in the db_index (it's not ever set anywhere); The string based check was definitely broken for me
• Also update pgx imports to the yugabyte one so that ErrNoRows checks work correctly

Proposed Changes

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