Hide rpc headers when list networks with stellar network ls --long.

[fnando]

What

$ target/debug/stellar network ls --long
Name: mynet
RPC url: https://rpc.example.com
RPC headers:
  Authorization: <concealed>
Network passphrase: Test SDF Network ; September 2015

Name: prod
RPC url: https://mainnet.sorobanrpc.com
RPC headers: not set
Network passphrase: Public Global Stellar Network ; September 2015

Name: pubnet
RPC url: https://mainnet.sorobanrpc.com
RPC headers: not set
Network passphrase: Public Global Stellar Network ; September 2015

Name: test-net-headers
RPC url: http://localhost:8000/rpc
RPC headers:
  Authorization: <concealed>
  X-Api-Key: <concealed>
Network passphrase: Test Network

Name: local
RPC url: http://localhost:8000/rpc
RPC headers: not set
Network passphrase: Standalone Network ; February 2017

Name: futurenet
RPC url: https://rpc-futurenet.stellar.org:443
RPC headers: not set
Network passphrase: Test SDF Future Network ; October 2022

Name: mainnet
RPC url: Bring Your Own: https://developers.stellar.org/docs/data/rpc/rpc-providers
RPC headers: not set
Network passphrase: Public Global Stellar Network ; September 2015

Name: testnet
RPC url: https://soroban-testnet.stellar.org
RPC headers: not set
Network passphrase: Test SDF Network ; September 2015

Why

https://hackerone.com/reports/3596218

Known limitations

N/A

[Copilot]

Pull request overview

This PR updates the stellar network ls --long output to avoid leaking RPC header values by concealing them in the long listing, addressing the reported security issue.

Changes:

• Update network ls --long formatting to print RPC URL, passphrase, and RPC header names while concealing header values.
• Improve long listing readability by separating entries with a blank line.
• Add integration tests ensuring RPC header values are not printed and that “not set” is shown when no headers exist.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cmd/soroban-cli/src/commands/network/ls.rs	Reworks long network listing output to conceal RPC header values and adjusts entry separators.
cmd/crates/soroban-test/tests/it/integration/network.rs	Adds integration tests to validate concealed header output and “not set” behavior.