Parses and applies Arke permission filter strings.

TODO: this is a copy of ArkeServer.Utils.QueryFilters with conn replaced by project. The filter DSL parser belongs in arke or arke_auth as a shared util. Extract upstream and drop this module once that lands.

Filter syntax: eq(field,value), and(...), or(...), not(...), plus operator nodes (eq, contains, lte, gt, in, isnull, ...).