Add lifecycle management for Dial clients and pools

[kryachkow]

Name and Version

latest

What is the problem this feature will solve?

Dial, AsyncDial, DialClientPool, and AsyncDialClientPool should expose public lifecycle APIs for closing underlying HTTP clients.

What is the feature you are proposing to solve the problem?

Motivation

AsyncDial owns an internal httpx.AsyncClient, but there is no public aclose() or async context manager. Consumers currently need to close internals manually:

await dial._http_client.internal_http_client.aclose()

For pooled clients, AsyncDialClientPool also owns a shared httpx.AsyncClient, but does not expose aclose(), __aenter__, or __aexit__.

Proposed API

For sync clients and pools:

client.close()

with Dial(...) as client:
    ...

For async clients and pools:

await client.aclose()

async with AsyncDial(...) as client:
    ...

For pools:

pool.close()
await async_pool.aclose()

Use Case

Framework applications need deterministic shutdown without relying on private attributes or injecting and managing their own httpx client.

What alternatives have you considered?

No response