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/Cargo.lock

@@ -1655,6 +1655,14 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "obicompactvec"
+version = "0.1.0"
+dependencies = [
+ "memmap2",
+ "tempfile",
+]
+
 [[package]]
 name = "obidebruinj"
 version = "0.1.0"
@@ -1741,6 +1749,7 @@ dependencies = [
 name = "obilayeredmap"
 version = "0.1.0"
 dependencies = [
+ "cacheline-ef",
  "epserde 0.8.0",
  "memmap2",
  "obikseq",