Add TOML persistence support for KmerSet and KmerSetGroup

This commit adds support for saving and loading KmerSet and KmerSetGroup structures using TOML, YAML, and JSON formats for metadata. It includes:

- Added github.com/pelletier/go-toml/v2 dependency
- Implemented Save and Load methods for KmerSet and KmerSetGroup
- Added metadata persistence with support for multiple formats (TOML, YAML, JSON)
- Added helper functions for format detection and metadata handling
- Updated version commit hash

pkg/obioptions/version.go

@@ -8,7 +8,7 @@ import (
 // corresponds to the last commit, and not the one when the file will be
 // commited
 
-var _Commit = "60f27c1"
+var _Commit = "aa468ec"
 var _Version = "Release 4.4.0"
 
 // Version returns the version of the obitools package.