Introduce structured error types and bump Go/linter versions

Replace ad-hoc fmt.Errorf/errors.New calls with typed error structs across config, sarin, and script packages to enable type-based error handling. Add script-specific error handlers in CLI entry point. Fix variable shadowing bug in Worker for scriptTransformer. Bump Go to 1.25.7 and golangci-lint to v2.8.0.

internal/types/proxy.go

@@ -1,7 +1,6 @@
 package types
 
 import (
-	"fmt"
 	"net/url"
 )
 
@@ -17,6 +16,9 @@ func (proxies *Proxies) Append(proxy ...Proxy) {
 	*proxies = append(*proxies, proxy...)
 }
 
+// Parse parses a raw proxy string and appends it to the list.
+// It can return the following errors:
+//   - ProxyParseError
 func (proxies *Proxies) Parse(rawValue string) error {
 	parsedProxy, err := ParseProxy(rawValue)
 	if err != nil {
@@ -27,10 +29,13 @@ func (proxies *Proxies) Parse(rawValue string) error {
 	return nil
 }
 
+// ParseProxy parses a raw proxy URL string into a Proxy.
+// It can return the following errors:
+//   - ProxyParseError
 func ParseProxy(rawValue string) (*Proxy, error) {
 	urlParsed, err := url.Parse(rawValue)
 	if err != nil {
-		return nil, fmt.Errorf("failed to parse proxy URL: %w", err)
+		return nil, NewProxyParseError(err)
 	}
 
 	proxyParsed := Proxy(*urlParsed)