feat(obikmer): add index subcommand for kmer counting pipeline

Introduce the `index` CLI subcommand, implementing a resumable, multi-stage pipeline to partition, dereplicate, and count kmers from input sequences. The command builds a layered de Bruijn graph index per partition, applies optional abundance filtering, and persists unitigs alongside an MPHF-based count matrix. Update `Cargo.toml` and `Cargo.lock` to include new dependencies (`epserde`, `ptr_hash`, `cacheline-ef`, `obicompactvec`, `obilayeredmap`) required for the index builder, and refresh the profiling data files.

src/Cargo.lock

@@ -1760,15 +1760,19 @@ dependencies = [
 name = "obikmer"
 version = "0.1.0"
 dependencies = [
+ "cacheline-ef",
  "clap",
+ "epserde 0.8.0",
  "indicatif",
  "memmap2",
  "niffler 3.0.0",
+ "obicompactvec",
  "obidebruinj",
  "obifastwrite",
  "obikpartitionner",
  "obikrope",
  "obikseq",
+ "obilayeredmap",
  "obipipeline",
  "obiread",
  "obiskbuilder",
@@ -1776,6 +1780,7 @@ dependencies = [
  "obisys",
  "ph",
  "pprof",
+ "ptr_hash",
  "rayon",
  "tracing",
  "tracing-subscriber",