feat(client): Optionally enable asynchronous DNS resolver

[0x676e67]

This pull request introduces several important changes to the rnet project, focusing on the addition of an asynchronous DNS resolver and improvements to the existing codebase. The most significant changes include modifications to the Cargo.toml dependencies, updates to the Client struct to support async DNS, and the addition of a new dns module.

Client Enhancements:

• src/client.rs: Imported the dns module and added async DNS resolver initialization in the Client struct. [1] [2] [3] [4]
• examples/client.py: Enabled async_dns in the Client initialization.

New DNS Module:

• src/dns.rs: Added a new module to handle DNS resolution with a function to initialize a global DNS resolver using the HickoryDnsResolver and LookupIpStrategy.

Error Handling:

• src/error.rs: Introduced a new DNSResolverError exception to handle DNS resolver initialization errors.

Parameter Updates:

• src/param/client.rs: Updated ClientParams to include the async_dns option and modified the FromPyObject implementation to extract this new option. [1] [2]

Module Integration:

• src/lib.rs: Integrated the new dns module.