refactor: move pkg/ to internal/ and update imports

Restructure project by relocating package contents from pkg/ to internal/ to better reflect internal-only usage. This commit is initial step to prepare project for public api

internal/build/source_downloader.go

@@ -0,0 +1,86 @@
+// ALR - Any Linux Repository
+// Copyright (C) 2025 The ALR Authors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package build
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"strings"
+
+	"gitea.plemya-x.ru/Plemya-x/ALR/internal/dl"
+	"gitea.plemya-x.ru/Plemya-x/ALR/internal/dlcache"
+)
+
+type SourceDownloader struct {
+	cfg Config
+}
+
+func NewSourceDownloader(cfg Config) *SourceDownloader {
+	return &SourceDownloader{
+		cfg,
+	}
+}
+
+func (s *SourceDownloader) DownloadSources(
+	ctx context.Context,
+	input *BuildInput,
+	basePkg string,
+	si SourcesInput,
+) error {
+	for i, src := range si.Sources {
+
+		opts := dl.Options{
+			Name:        fmt.Sprintf("[%d]", i),
+			URL:         src,
+			Destination: getSrcDir(s.cfg, basePkg),
+			Progress:    os.Stderr,
+			LocalDir:    getScriptDir(input.script),
+		}
+
+		if !strings.EqualFold(si.Checksums[i], "SKIP") {
+			// Если контрольная сумма содержит двоеточие, используйте часть до двоеточия
+			// как алгоритм, а часть после как фактическую контрольную сумму.
+			// В противном случае используйте sha256 по умолчанию с целой строкой как контрольной суммой.
+			algo, hashData, ok := strings.Cut(si.Checksums[i], ":")
+			if ok {
+				checksum, err := hex.DecodeString(hashData)
+				if err != nil {
+					return err
+				}
+				opts.Hash = checksum
+				opts.HashAlgorithm = algo
+			} else {
+				checksum, err := hex.DecodeString(si.Checksums[i])
+				if err != nil {
+					return err
+				}
+				opts.Hash = checksum
+			}
+		}
+
+		opts.DlCache = dlcache.New(s.cfg)
+
+		err := dl.Download(ctx, opts)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}