Add stellar network id to return the network id.

[fnando]

What

# Defaults to testnet, as every other command
$ stellar network id
cee0302d59844d32bdca915c8203dd44b33fbb7edc19051ea37abedf28ecd472

# Respects default network
$ stellar network use local
ℹ️ The default network is set to `local`

$ stellar network id
baefd734b8d3e48472cff83912375fedbc7573701912fe308af730180f97d74a

# Explicit usage
$ stellar network id --network testnet
cee0302d59844d32bdca915c8203dd44b33fbb7edc19051ea37abedf28ecd472

# Formatted JSON
$ stellar network id --output json-formatted
{
  "id": "baefd734b8d3e48472cff83912375fedbc7573701912fe308af730180f97d74a",
  "network_passphrase": "Standalone Network ; February 2017"
}

# One-line JSON
$ stellar network id --output json
{"id":"baefd734b8d3e48472cff83912375fedbc7573701912fe308af730180f97d74a","network_passphrase":"Standalone Network ; February 2017"}

Why

Implement #2390.

Known limitations

N/A

[Copilot]

Pull request overview

This PR adds a new stellar network id command that outputs the network ID (SHA-256 hash of the network passphrase), implementing issue #2390. This command addresses a common pain point where users had to manually compute the network ID using shell tools like sha256sum, which was error-prone.

Changes:

• Adds a new stellar network id subcommand with support for plain text and JSON output formats
• Integrates the command into the network module with proper error handling
• Includes a basic integration test to verify the command works with testnet
• Updates the CLI documentation with the new command usage

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
cmd/soroban-cli/src/commands/network/mod.rs	Registers the new id subcommand in the network module enum and error handling
cmd/soroban-cli/src/commands/network/id.rs	Implements the network ID command with SHA-256 hashing and multiple output formats
cmd/crates/soroban-test/tests/it/integration/network.rs	Adds integration test to verify the network ID command works correctly
FULL_HELP_DOCS.md	Documents the new command including options and usage examples

[leighmcculloch]

# Formatted JSON
$ stellar network id --output json-formatted
{
  "id": "baefd734b8d3e48472cff83912375fedbc7573701912fe308af730180f97d74a",
  "network_passphrase": "Standalone Network ; February 2017"
}

Maybe this command should be stellar network info that returns a bundle of information. Or, we should add another command stellar network passphrase that returns just the phassphrase text.