fix: accept documented RelayClient constructor aliases

[binggao1230]

Summary

• accept the documented host, chain, and signer keyword aliases in RelayClient.__init__
• preserve the existing relayer_url, chain_id, and private_key API, with existing names taking precedence
• keep documented relayer API key fields on the client so the setup snippet no longer fails at construction

Fixes #25.

Tests

• uv run --with-requirements requirements.txt pytest tests/test_client_deposit_wallet.py -q
• uv run --with-requirements requirements.txt pytest -q

---

Note

Low Risk
Constructor-only compatibility change with explicit validation; no changes to relay execution or auth header logic.

Overview
RelayClient.__init__ now accepts documented keyword aliases host, chain, and signer (keyword-only) as fallbacks when relayer_url, chain_id, and private_key are omitted. Existing parameter names still win when both are passed.

Construction requires a relayer URL and chain id after alias resolution; missing values raise TypeError. relayer_api_key and relayer_api_key_address are accepted and stored on the client instance.

Tests cover alias-based construction (including trailing-slash URL normalization) and precedence of canonical names over aliases.

^{Reviewed by Cursor Bugbot for commit f7b27a0. Bugbot is set up for automated code reviews on this repo. Configure here.}