Read every setting through viper and rename the settings (closes #211)

Every setting of discriminator and rproxy is read through viper, in place
of the os.LookupEnv function Main passed down. NewViper turns AutomaticEnv
and AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.

The settings are renamed. Discriminator's take the prefix SWW_WAF_,
rproxy's take SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core
Rule Set's settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.

Model: deepseek-v4-pro (first version); opus-5-5 (rework)

internal/rproxy/rproxy_test.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"sneak.berlin/go/smallwebwaf/internal/config"
+	"sneak.berlin/go/smallwebwaf/internal/config/configtest"
 	"sneak.berlin/go/smallwebwaf/internal/discriminator"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 	"sneak.berlin/go/smallwebwaf/internal/rproxy"
@@ -43,13 +44,13 @@ const (
 
 // The settings the tests set.
 const (
-	timeoutSetting     = "SWRP_TIMEOUT_MS"
-	defaultDisposition = "SWRP_DEFAULT_DISPOSITION"
-	trustedProxies     = "SWRP_TRUSTED_PROXIES"
-	maxRequestSize     = "SWRP_MAX_REQUEST_SIZE"
-	maxResponseSize    = "SWRP_MAX_RESPONSE_SIZE"
-	maxRequestTime     = "SWRP_MAX_REQUEST_TIME_MS"
-	maxResponseTime    = "SWRP_MAX_RESPONSE_TIME_MS"
+	timeoutSetting     = "SWW_RPROXY_TIMEOUT_MS"
+	defaultDisposition = "SWW_RPROXY_DEFAULT_DISPOSITION"
+	trustedProxies     = "SWW_RPROXY_TRUSTED_PROXIES"
+	maxRequestSize     = "SWW_RPROXY_MAX_REQUEST_SIZE"
+	maxResponseSize    = "SWW_RPROXY_MAX_RESPONSE_SIZE"
+	maxRequestTime     = "SWW_RPROXY_MAX_REQUEST_TIME_MS"
+	maxResponseTime    = "SWW_RPROXY_MAX_RESPONSE_TIME_MS"
 )
 
 // The headers the tests set and look at.
@@ -354,15 +355,11 @@ func startServerLogging(
 	t.Helper()
 
 	settings := map[string]string{
-		"SWRP_WAF_BACKEND": backend, "SWRP_UPSTREAM_URL": appURL,
+		"SWW_RPROXY_WAF_BACKEND": backend, "SWW_RPROXY_UPSTREAM_URL": appURL,
 	}
 	maps.Copy(settings, env)
 
-	cfg, err := config.RProxyFromEnvironment(func(name string) (string, bool) {
-		value, ok := settings[name]
-
-		return value, ok
-	})
+	cfg, err := config.RProxyFromEnvironment(configtest.Viper(settings))
 	if err != nil {
 		t.Fatalf("settings %v: %v", settings, err)
 	}