refactor: cve5 conversion to be more modular and extensible per CNA (#4094)

This PR:
- Moves the cve5 conversion code out of the cmd folder
- creates a common.go folder for reused/common functions by the
conversion
- initializes a factory-based design pattern for CNA based version
extraction methods
    - Linux has its own extractor now
- downside of this is that we may have to maintain multiple versions of
the extractions, but we'll mitigate this by making sure code that is
doing the same thing is abstracted into its own function.
- splits apart some of the version extraction patterns into their own
functions.

Author: jess-lowe

vulnfeeds/cmd/cve-bulk-converter/main.go

@@ -11,7 +11,7 @@ import (
 	"strings"
 	"sync"
 
-	"github.com/google/osv/vulnfeeds/cmd/cvelist2osv"
+	"github.com/google/osv/vulnfeeds/cvelist2osv"
 	"github.com/google/osv/vulnfeeds/cves"
 	"github.com/google/osv/vulnfeeds/utility/logger"
 )

vulnfeeds/cmd/cve-single-converter/main.go

@@ -7,7 +7,7 @@ import (
 	"log/slog"
 	"os"
 
-	"github.com/google/osv/vulnfeeds/cmd/cvelist2osv"
+	"github.com/google/osv/vulnfeeds/cvelist2osv"
 	"github.com/google/osv/vulnfeeds/cves"
 	"github.com/google/osv/vulnfeeds/utility/logger"
 )