PIP-121: Introduce ServiceInfoProvider to update service info dynamically

[BewareMyPower]

The design is a bit different from Java client's ServiceUrlProvider because the internal classes (e.g. ClientImpl) in C++ client are not exposed unlike the Java client.

Differences:

• The service URL, authentication and TLS trust file are coupled into a ServiceInfo struct. Otherwise, the interface could be complicated, for example, Java's AutoClusterFailoverBuilder accepts 3 methods for this purpose (secondary, secondaryAuthentication and secondaryTlsTrustCertsFilePath).
• The ServiceUrlProvider#getServiceUrl is replaced by the getServiceInfo method added to Client.
• The initialize method accepts a onServiceInfoUpdate callback that is used to update the service info. This can avoid adding a new public method to Client by passing an internal method of ClientImpl as the callback.
• The probe logic should be implemented independently.

Breaking changes:

• Since now some fields of ClientConfiguration can be modified dynamically, remove these public getters because they might return outdated values. Now it should be checked from Client::getServiceInfo.
• The setUseTls method is removed as well because it should never be set by users. Whether to use TLS is actually determined by the service URL's scheme (e.g. pulsar+ssl:// prefix)

[Copilot]

Pull request overview

Adds a public API to dynamically switch a Client instance to a different Pulsar cluster at runtime (service URL + auth + TLS trust certs), and refactors internal lookup/connection usage so in-flight components pick up the new cluster after switching.

Changes:

• Introduce ServiceInfo, Client::updateServiceInfo(...), and Client::getServiceInfo() to support application-managed cluster failover.
• Refactor internal components (lookup/schema/partition metadata calls) to route through ClientImpl accessors guarded by a shared mutex, so lookup service updates are visible everywhere.
• Add/extend tests to validate cluster switching and expose token helper for reuse.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/LookupServiceTest.cc	Updates tests to use ClientImpl lookup/schema accessors instead of exposing LookupService directly.
tests/ClientTest.cc	Adds testUpdateServiceInfo validating switching between clusters with different auth/TLS settings.
tests/AuthTokenTest.cc	Makes getToken() non-static so it can be reused by the new client test.
lib/ReaderImpl.cc	Stops passing a fixed LookupService into consumers; relies on client accessors instead.
lib/PatternMultiTopicsConsumerImpl.h	Updates ctor signature to remove LookupServicePtr dependency.
lib/PatternMultiTopicsConsumerImpl.cc	Routes namespace topic discovery via ClientImpl so lookups reflect cluster switches.
lib/PartitionedProducerImpl.h	Removes stored LookupServicePtr member.
lib/PartitionedProducerImpl.cc	Fetches partition metadata via ClientImpl accessor to respect cluster switches.
lib/MultiTopicsConsumerImpl.h	Removes stored LookupServicePtr member and adjusts ctors accordingly.
lib/MultiTopicsConsumerImpl.cc	Fetches partition metadata via ClientImpl accessor; adds client weak-lock checks.
lib/ConsumerImpl.h	Adds onClusterSwitching() hook and preserves original start message id from config.
lib/ConsumerImpl.cc	Implements onClusterSwitching() to reset some consumer state when switching clusters.
lib/ConnectionPool.h	Adds resetForClusterSwitching(...) to close existing conns but keep pool usable.
lib/ConnectionPool.cc	Implements pool reset, closing connections with a “switch cluster” flag.
lib/ClientImpl.h	Adds shared-mutex guarded lookup/schema/partition APIs + service info update/get.
lib/ClientImpl.cc	Implements updateServiceInfo() and getServiceInfo(), rebuilds lookup service on switch.
lib/ClientConnection.h	Extends close() signature with switchCluster flag (defaulted).
lib/ClientConnection.cc	On cluster-switch close, notifies consumers via onClusterSwitching().
lib/Client.cc	Exposes new public methods and routes schema calls through ClientImpl wrapper.
include/pulsar/Client.h	Adds public ServiceInfo struct + Client API for updating/getting service info.

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