feat: add resolveAll through Netty's configured resolver (DRIVER-201)

[nikagra]

Groundwork for expanding a contact-point hostname to every address it resolves to (next PR in the stack): nothing in the driver can ask Netty's configured resolver for all the addresses of a name, only for one, and only inside Bootstrap.connect().

• ChannelFactory.resolveAll(SocketAddress) builds a bootstrap the way connect() does, runs NettyOptions.afterBootstrapInitialized on it, and asks the resolver that hook left installed, so a custom AddressResolverGroup is honoured.
• The lookup runs on one pinned I/O event loop, never on the calling thread: AddressResolver#resolveAll resolves inline, and the default resolver blocks on the JDK lookup. A connect already pays that on an event loop, so this is parity, and the admin executor is left free.
• The hook is asked once, not per lookup — one shaped bootstrap.resolver(new DnsAddressResolverGroup(...)) would otherwise mint a resolver, a socket and an empty DNS cache every time.
• Netty's own short-circuits are mirrored: a disabled resolver, an unsupported address or one already resolved comes back as is, as the only element. Otherwise the resolver's answer is returned verbatim, immutable; a failure fails the stage, nothing throws, and no path can leave the stage incomplete.
• No caller yet, no change to connect().

Verified: ChannelFactoryResolveAllTest (13 cases), the thread and hook-count cases proven red against the pre-change file; every existing ChannelFactory*Test unmodified and green; full core unit suite green (3981) on JDK 11. Not covered: no integration test — the caller in the next PR carries those.

Stacked on #1065 (s2/05-fallback-default); the first commit here is that PR's.

Refs: #890, #215

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