feat: add benchmark pipeline, expose APIs, and enforce strict paths

Introduces a Make-based orchestration for simulating, indexing, merging, filtering, and verifying k-mer counts and presence. Exposes internal builder and iterator APIs publicly, enforces mandatory leading slashes for predicate patterns, registers the `obitaxonomy` crate, and updates tooling configurations alongside documentation.

docmd/implementation/filtering.md

@@ -29,16 +29,17 @@ Multiple values separated by `|` are always OR-ed within the predicate.
 
 ### Path matching (`~` and `!~`)
 
-Metadata values can represent hierarchical taxonomic paths such as
+Metadata values can represent hierarchical concept paths such as
 `/Eukaryota/Viridiplantae/Streptophyta/Betulaceae/Betula/nana`.
 
-- **Absolute pattern** (starts with `/`): the value must start with the pattern
-  at a segment boundary.
-  `taxon~/Betulaceae/Betula` matches `/Betulaceae/Betula/nana` and
+**Both the stored metadata value and the pattern must start with `/`.**
+A pattern that does not start with `/` is rejected at parse time with an error.
+
+The value matches the pattern if it equals it exactly or starts with the pattern
+followed by `/` (segment-boundary prefix):
+
+- `taxon~/Betulaceae/Betula` matches `/Betulaceae/Betula/nana` and
   `/Betulaceae/Betula` but not `/Betulaceae/Betuloides/…`.
-- **Bare segment** (no leading `/`): the value must contain the pattern as an
-  exact path component anywhere.
-  `taxon~Betula` matches any path that has `Betula` as one of its segments.
 
 ### Missing metadata key → NA