Deploy v0.14 counter contract on testnet once testnet upgrades; update counter_contract_increment address

## Context

`counter_contract_increment.rs` (and related docs/web-client tutorials) reference a hardcoded counter contract address that was deployed with v0.14 tools on devnet.

AccountId is derived from the code commitment, which uses the Poseidon2 hash function in v0.14. This means:
- v0.13-deployed contract addresses are invalid for v0.14 clients (procedure hash mismatch)
- A v0.14 contract deployed with the **same deterministic seed** on testnet will produce `mtst1XYZ` (same suffix as `mdev1XYZ`)

## Required action (when testnet upgrades to v0.14)

1. Run `deploy_counter_deterministic.rs` with the same seed against testnet RPC
2. Verify the resulting address suffix matches the devnet deployment
3. Update the hardcoded address in `rust-client/src/bin/counter_contract_increment.rs` to the combined form (following the PR #177 pattern) so it works on both networks
4. Update the same address in any docs/web-client tutorials that reference it

## Note

`counter_contract_fpi.rs` is **not affected** — it deploys in-session and requires no hardcoded address.