txsim nice to haves

[rootulp]

Context

I've been using txsim to spam Mocha

Problems

1. txsim expects a --key-path as a CLI argument. We could make it optional and by default look in ~/.celestia-app
2. txsim populates N accounts with 1000 TIA which is wasteful. Using the --feegrant flag eliminates this problem but that's not mentioned in the example. Let's make the example command include the --feegrant flag
3. If you provide an incorrect GRPC endpoint, you get this confusing error:

{"level":"error","error":"error getting balance for celestia1rmqkyypuly8u5cp7ggrt5cj788887w2tadcvyu: rpc error: code = Unavailable desc = name resolver error: produced zero addresses","account":"tx-sim-9","time":"2025-01-14T14:13:00-05:00","message":"error getting initial account balance"}

Instead it should return an error that the GRPC endpoint isn't accessible

4. It's difficult to actually fill blocks on a testnet. It would be nice if txsim had a command to fill blocks so that users don't have to fiddle with the flags --blob, --blob-amounts, --blob-sizes

[rootulp]

Pretty sure txsim can't handle GRPC endpoints running on port 443. Every time I use a GRPC endpoint from https://github.com/celestiaorg/docs/blob/main/how-to-guides/mocha-testnet.md#community-grpc-endpoints I hit:

no suitable master account found%