feat: blockheight tool (#3761)

I used this tool to determine that the v2 upgrade height that we should
configure on Arabica is `1713503`.
Note: The target upgrade time on Arabica is approximately 2024-08-14 at
14:00:00 UTC.

tools/blockheight/README.md

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+# blockheight
+
+blockheight is a small tool to help predict the block height of a chain at a given time.
+
+## Usage
+
+```shell
+$ go run main.go https://rpc.celestia-arabica-11.com:443 2024-08-14T14:00:00
+chainID: arabica-11
+currentHeight: 1659839
+currentTime: 2024-08-07 13:33:15.331656793 +0000 UTC
+targetHeight: 1713503
+targetTime: 2024-08-14 14:00:00 +0000 UTC
+diffInSeconds: 606404
+diffInBlockHeight: 53664
+```

tools/blockheight/main.go

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+package main
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"os"
+	"time"
+
+	"github.com/tendermint/tendermint/rpc/client/http"
+)
+
+const (
+	// blockTime is the observed average time between blocks. You can update this
+	// value based on the block time on https://www.mintscan.io/celestia/block/ or
+	// the output from the blocktime tool.
+	blockTime = 11.30 // seconds between blocks for Arabica
+
+	// exampleNodeRPC is an example node RPC endpoint for the Arabica testnet.
+	exampleNodeRPC = "https://rpc.celestia-arabica-11.com:443"
+
+	// targetTime is an example target time for the block height prediction.
+	targetTime = "2024-08-14T14:00:00"
+
+	// layout is the expected time format for targetTime.
+	layout = "2006-01-02T15:04:05"
+)
+
+func main() {
+	if err := Run(); err != nil {
+		fmt.Printf("ERROR: %s", err.Error())
+	}
+}
+
+func Run() error {
+	if len(os.Args) < 3 {
+		fmt.Printf("Usage: %s <node_rpc> <target_time>\n", os.Args[0])
+		fmt.Printf("Example: %s %s %s\n", os.Args[0], exampleNodeRPC, targetTime)
+		return nil
+	}
+
+	_, nodeRPC, targetTimeArg := os.Args[0], os.Args[1], os.Args[2]
+	c, err := http.New(nodeRPC, "/websocket")
+	if err != nil {
+		return err
+	}
+	resp, err := c.Status(context.Background())
+	if err != nil {
+		return err
+	}
+	chainID := resp.NodeInfo.Network
+	currentHeight := resp.SyncInfo.LatestBlockHeight
+	currentTime := resp.SyncInfo.LatestBlockTime
+
+	targetTime, err := time.Parse(layout, targetTimeArg)
+	if err != nil {
+		return fmt.Errorf("error parsing target time: %v", err)
+	}
+
+	if currentTime.After(targetTime) {
+		return fmt.Errorf("current time %v is already after target time %v", currentTime, targetTime)
+	}
+
+	diffInSeconds := targetTime.Sub(currentTime).Seconds()
+	diffInBlockHeight := math.Floor(diffInSeconds / blockTime)
+	targetHeight := currentHeight + int64(diffInBlockHeight)
+
+	fmt.Printf("chainID: %v\n", chainID)
+	fmt.Printf("currentHeight: %v\n", currentHeight)
+	fmt.Printf("currentTime: %v\n", currentTime.String())
+	fmt.Printf("targetHeight: %v\n", targetHeight)
+	fmt.Printf("targetTime: %v\n", targetTime.String())
+	fmt.Printf("diffInSeconds: %v\n", math.Floor(diffInSeconds))
+	fmt.Printf("diffInBlockHeight: %v\n", diffInBlockHeight)
+	return nil
+}