Add stellar token symbol subcommand

[fnando]

What

Adds stellar token symbol, a read-only subcommand returning a token's SEP-41 symbol() metadata. Resolves a token by --id (contract id, alias, native, or CODE:ISSUER) and prints the symbol as text or JSON.

Why

Part of #2620 (typed SEP-41 + SAC client), following name. Stacked on the token-name branch; a thin wrapper over contract invoke reusing args::invoke_by_position and args::not_deployed_error.

Known limitations

N/A

[Copilot]

Pull request overview

Adds stellar token symbol for querying SEP-41 symbol metadata.

Changes:

• Adds read-only symbol invocation with text/JSON output.
• Integrates command routing and structured errors.
• Adds help documentation and integration tests.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
FULL_HELP_DOCS.md	Documents the symbol command.
cmd/soroban-cli/src/commands/token/symbol.rs	Implements symbol querying and output.
cmd/soroban-cli/src/commands/token/mod.rs	Registers and dispatches the command.
cmd/soroban-cli/src/cli.rs	Enables structured JSON errors.
cmd/crates/soroban-test/tests/it/integration/token/symbol.rs	Tests SAC symbols and deployment errors.
cmd/crates/soroban-test/tests/it/integration/token/mod.rs	Registers symbol integration tests.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.