Refactor fetch and pacman packages into subpackages

Split fetch into alpm and aur subpackages for better organization.
Rename state to log. Split pacman into read and sync subpackages.
Remove validation in favor of read.DBFreshness.

pkg/fetch/aur/aur.go

@@ -0,0 +1,94 @@
+package aur
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"time"
+)
+
+var AURInfoURL = "https://aur.archlinux.org/rpc?v=5&type=info"
+
+type Package struct {
+	Name        string `json:"Name"`
+	PackageBase string `json:"PackageBase"`
+	Version     string `json:"Version"`
+	URL         string `json:"URL"`
+}
+
+type Response struct {
+	Results []Package `json:"results"`
+}
+
+type Client struct {
+	cache map[string]Package
+}
+
+func New() *Client {
+	return &Client{
+		cache: make(map[string]Package),
+	}
+}
+
+func (c *Client) Fetch(packages []string) (map[string]Package, error) {
+	start := time.Now()
+	fmt.Fprintf(os.Stderr, "[debug] aur.Fetch: starting...\n")
+
+	result := make(map[string]Package)
+
+	if len(packages) == 0 {
+		return result, nil
+	}
+
+	var uncached []string
+	for _, pkg := range packages {
+		if _, ok := c.cache[pkg]; !ok {
+			uncached = append(uncached, pkg)
+		}
+	}
+
+	if len(uncached) == 0 {
+		fmt.Fprintf(os.Stderr, "[debug] aur.Fetch: done (cached) (%.2fs)\n", time.Since(start).Seconds())
+		for _, pkg := range packages {
+			result[pkg] = c.cache[pkg]
+		}
+		return result, nil
+	}
+
+	v := url.Values{}
+	for _, pkg := range packages {
+		v.Add("arg[]", pkg)
+	}
+
+	resp, err := http.Get(AURInfoURL + "&" + v.Encode())
+	if err != nil {
+		return result, err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return result, err
+	}
+
+	var aurResp Response
+	if err := json.Unmarshal(body, &aurResp); err != nil {
+		return result, err
+	}
+
+	for _, r := range aurResp.Results {
+		c.cache[r.Name] = r
+		result[r.Name] = r
+	}
+
+	fmt.Fprintf(os.Stderr, "[debug] aur.Fetch: done (%.2fs)\n", time.Since(start).Seconds())
+	return result, nil
+}
+
+func (c *Client) Get(name string) (Package, bool) {
+	pkg, ok := c.cache[name]
+	return pkg, ok
+}