Add stellar contract info wasm-hash command

[Copilot]

This PR adds a new wasm-hash subcommand to stellar contract info that outputs the WASM hash for a given contract or WASM file.

Changes

• New subcommand: stellar contract info wasm-hash
• Input sources: Accepts --wasm, --wasm-hash, or --contract-id (same as other info commands)
• Output: Hex-encoded WASM hash to stdout
• Error handling: Proper error for stellar asset contracts

Implementation

• Added wasm_hash.rs module following existing patterns in cmd/soroban-cli/src/commands/contract/info/
• Integrated with existing shared infrastructure for contract data fetching
• Uses crate::utils::contract_hash() for consistent hash calculation
• Added comprehensive unit tests including verification with real WASM fixtures

Usage

# From local WASM file
$ stellar contract info wasm-hash --wasm ./contract.wasm

# From contract ID on network  
$ stellar contract info wasm-hash --network testnet --contract-id CDSJWGUPY2HFHYNLT3EZX7YGJ4X7YMWPQWHHGNKB6IVH6WRXAJFI7627
283f8e42a3585aa3a511c06c7d09a94d66762773cdf493cc4afc455d7b68adcf

# From existing WASM hash
$ stellar contract info wasm-hash --wasm-hash 283f8e42a3585aa3a511c06c7d09a94d66762773cdf493cc4afc455d7b68adcf
283f8e42a3585aa3a511c06c7d09a94d66762773cdf493cc4afc455d7b68adcf

This provides a convenient way for developers to retrieve WASM hashes without the complex RPC + XDR decoding workflow described in the issue.

Fixes #1877.

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[leighmcculloch]

I think the code being added for this is not ideal. The --wasm-hash param is still present because it is part of the shared args. Also, in some cases it downloads the wasm unnecessarily even though it could just stop at getting the hash for the contract instance entry.

Given the low importance of this command, and the smaller maintenance burden it is to reuse the other info subcommands shared code that does those not perfect things, I think this is fine as is and preferred over creating bespoke code that does exactly what's needed for this.