Add obikselect crate for k-mer selection and aggregation

Introduces a new `obikselect` module to handle k-mer selection and column aggregation. Adds a `select` CLI command in `obikmer2` that supports group predicates, aggregate operators, and output column filtering. Implements operator parsing with case-insensitive matching and default rules, along with a centralized module for resolving group specifications from metadata or genome filters. Updates dependencies to include the new crate and its prerequisites.

src/obikselect/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 obikindex     = { path = "../obikindex" }
+obikfilter    = { path = "../obikfilter" }
 obikalgorithm = { path = "../obikalgorithm" }
 obicompactvec = { path = "../obicompactvec" }
 obisys        = { path = "../obisys" }