Add persistent compact integer vector and cache-line-optimized MPHF

Introduce the `obicompactvec` crate, featuring a two-tier, memory-mapped integer vector that uses a primary `u8` array with a sentinel for overflow dispatch and a sparse L1-resident index for fast random access. Implement builder and reader modules with zero-copy serialization and comprehensive test coverage. Update `obilayeredmap` to replace the default hash function with a cache-line-optimized `Mphf`, adding explicit bounds checking and duplicate-slot detection. Add documentation for both modules and update project configuration files accordingly.

src/obilayeredmap/Cargo.toml

@@ -4,14 +4,15 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-obikseq  = { path = "../obikseq" }
-obiskio  = { path = "../obiskio" }
-ptr_hash = "1.1"
-epserde  = "0.8"
-rayon    = "1"
-memmap2  = "0.9"
-serde      = { version = "1", features = ["derive"] }
-serde_json = "1"
+obikseq      = { path = "../obikseq" }
+obiskio      = { path = "../obiskio" }
+ptr_hash     = "1.1"
+cacheline-ef = "1.1"
+epserde      = "0.8"
+rayon        = "1"
+memmap2      = "0.9"
+serde        = { version = "1", features = ["derive"] }
+serde_json   = "1"
 
 [dev-dependencies]
 tempfile = "3"