refactor: implement RoutableSuperKmer and update k-mer indexing pipeline

Replace raw SuperkMer routing with a new RoutableSuperKimer type that embeds canonical sequences and precomputed minimizers, enabling direct partition routing via hash. Update the build pipeline to yield RoutableSuperKmers throughout (builder, scatterer), refactor FASTA/unitig export commands to use the new type and compressed outputs (.fasta.gz, .unitigs.fasta.zst), revise SuperKmer header to store n_kmers instead of seql (avoiding 256-byte wrap), and update documentation to reflect minimizer-based theory, two evidence-encoding strategies for unitig-MPHF indexing (global offset vs. ID+rank), and the new obipipeline library architecture with parallel workers, biased scheduling, and error handling.

src/Cargo.lock

@@ -1590,6 +1590,9 @@ name = "obikmer"
 version = "0.1.0"
 dependencies = [
  "clap",
+ "memmap2",
+ "niffler 3.0.0",
+ "obidebruinj",
  "obifastwrite",
  "obikpartitionner",
  "obikrope",
@@ -1597,7 +1600,10 @@ dependencies = [
  "obipipeline",
  "obiread",
  "obiskbuilder",
+ "obiskio",
+ "ph",
  "pprof",
+ "rayon",
  "tracing",
  "tracing-subscriber",
 ]
@@ -1633,6 +1639,8 @@ version = "0.1.0"
 dependencies = [
  "bitvec",
  "criterion2",
+ "serde",
+ "serde_json",
  "xxhash-rust",
 ]