_example: add zerovalue example and test

Author: arl

_example/zerovalue/go.mod

@@ -0,0 +1,11 @@
+module example/default
+
+go 1.23.0
+
+toolchain go1.24.5
+
+require github.com/arl/statsviz v0.7.1
+
+require github.com/gorilla/websocket v1.5.3 // indirect
+
+replace github.com/arl/statsviz => ../../

_example/zerovalue/go.sum

@@ -0,0 +1,8 @@
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/rogpeppe/go-internal v1.14.1 h1:UQB4HGPB6osV0SQTLymcB4TgvyWu6ZyliaW0tI/otEQ=
+github.com/rogpeppe/go-internal v1.14.1/go.mod h1:MaRKkUm5W0goXpeCfT7UZI6fk/L7L7so1lCWt35ZSgc=
+golang.org/x/sys v0.35.0 h1:vz1N37gP5bs89s7He8XuIYXpyY0+QlsKmzipCbUtyxI=
+golang.org/x/sys v0.35.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/tools v0.36.0 h1:kWS0uv/zsvHEle1LbV5LE8QujrxB3wfQyxHfhOk0Qkg=
+golang.org/x/tools v0.36.0/go.mod h1:WBDiHKJK8YgLHlcQPYQzNCkUxUypCaa5ZegCVutKm+s=

_example/zerovalue/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/arl/statsviz"
+	example "github.com/arl/statsviz/_example"
+)
+
+func main() {
+	// Force the GC to work to make the plots "move".
+	go example.Work()
+
+	// Register with the Server zero value.
+	var ss statsviz.Server
+	ss.Register(http.DefaultServeMux)
+
+	fmt.Println("Point your browser to http://localhost:8079/debug/statsviz/")
+	log.Fatal(http.ListenAndServe(":8079", nil))
+}

zerovalue.txt

@@ -0,0 +1,10 @@
+cp $STATSVIZ_ROOT/_example/default/main.go .
+cp $STATSVIZ_ROOT/_example/default/go.mod .
+
+go mod edit -replace=github.com/arl/statsviz=$STATSVIZ_ROOT
+go mod edit -replace=github.com/arl/statsviz/_example=$STATSVIZ_ROOT/_example
+go mod tidy
+
+go build main.go
+! exec ./main &
+checkui http://localhost:8079/debug/statsviz/