Add per-request DNS override API (curl --resolve / OkHttp Dns-style)

Could you please add support for a per-request DNS override that behaves like curl’s --resolve, or similar to OkHttp’s pluggable Dns interface (which lets you override host→IP
resolution on a per-request basis)? At the moment HTTPClient.Configuration.dnsOverride is the only entry-point, so the mapping is effectively static for the lifetime of a client. In
our workloads the host→IP mapping can change every minute, and paying the cost of creating and shutting down separate HTTPClient instances (each with its own connection pool) just to
apply a new override is prohibitively expensive.

The capability we are looking for is:

• Let a single request supply a temporary host→IP mapping (or a resolver callback).
• Keep using the original host for SNI/certificate validation and logging.
• Route the actual TCP/TLS connection to the overridden address.

If the existing execute APIs exposed an optional per-request override, or allowed callers to provide a resolver closure (akin to overriding OkHttp’s Dns.resolve), we could keep the
default behavior while enabling dynamic overrides. We’d greatly appreciate this enhancement.

Start by reading HTTPClient.Configuration.dnsOverride and the existing execute APIs mentioned in the issue. Determine how a per-request mapping or resolver would reach connection establishment while preserving the original host for SNI, certificate validation, and logging. Done means one client can issue requests with changing overrides without recreating its connection pool.