Split code into modules

This is a massive commit that restructures the code into modules:

db/
    All functions related to modifying the Database

types/
    All type definitions and methods that can be exclusivly used on
    these types without dependencies

policy/
    All Policy related code, now without dependencies on the Database.

policy/matcher/
    Dedicated code to match machines in a list of FilterRules

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/types/routes.go

@@ -0,0 +1,71 @@
+package types
+
+import (
+	"fmt"
+	"net/netip"
+
+	v1 "github.com/juanfont/headscale/gen/go/headscale/v1"
+	"google.golang.org/protobuf/types/known/timestamppb"
+	"gorm.io/gorm"
+)
+
+var (
+	ExitRouteV4 = netip.MustParsePrefix("0.0.0.0/0")
+	ExitRouteV6 = netip.MustParsePrefix("::/0")
+)
+
+type Route struct {
+	gorm.Model
+
+	MachineID uint64
+	Machine   Machine
+	Prefix    IPPrefix
+
+	Advertised bool
+	Enabled    bool
+	IsPrimary  bool
+}
+
+type Routes []Route
+
+func (r *Route) String() string {
+	return fmt.Sprintf("%s:%s", r.Machine, netip.Prefix(r.Prefix).String())
+}
+
+func (r *Route) IsExitRoute() bool {
+	return netip.Prefix(r.Prefix) == ExitRouteV4 || netip.Prefix(r.Prefix) == ExitRouteV6
+}
+
+func (rs Routes) Prefixes() []netip.Prefix {
+	prefixes := make([]netip.Prefix, len(rs))
+	for i, r := range rs {
+		prefixes[i] = netip.Prefix(r.Prefix)
+	}
+
+	return prefixes
+}
+
+func (rs Routes) Proto() []*v1.Route {
+	protoRoutes := []*v1.Route{}
+
+	for _, route := range rs {
+		protoRoute := v1.Route{
+			Id:         uint64(route.ID),
+			Machine:    route.Machine.Proto(),
+			Prefix:     netip.Prefix(route.Prefix).String(),
+			Advertised: route.Advertised,
+			Enabled:    route.Enabled,
+			IsPrimary:  route.IsPrimary,
+			CreatedAt:  timestamppb.New(route.CreatedAt),
+			UpdatedAt:  timestamppb.New(route.UpdatedAt),
+		}
+
+		if route.DeletedAt.Valid {
+			protoRoute.DeletedAt = timestamppb.New(route.DeletedAt.Time)
+		}
+
+		protoRoutes = append(protoRoutes, &protoRoute)
+	}
+
+	return protoRoutes
+}