Bump the C++ standard to 17

[BewareMyPower]

• Replace boost::optional with std::optional
• Replace boost::any with std::any
• Use std::weak_from_this to create a weak_ptr from a shared_ptr
• Leverage initializers for if to simplify code

Set the next major version to 4.0.0 for this change. If there are still demands from community for C++11 based build, we can consider 3.x.y releases.

[Copilot]

Pull request overview

This PR upgrades the C++ standard requirement from C++11 to C++17 for the Pulsar C++ client library, bumping the version to 4.0.0-pre. The upgrade modernizes the codebase by replacing Boost types with their standard library equivalents and leveraging C++17 language features for cleaner, more maintainable code.

Key Changes:

• Replaced boost::optional with std::optional and boost::any with std::any throughout the codebase
• Adopted std::weak_from_this() for creating weak pointers from shared_from_this()
• Introduced if-initializers to reduce variable scope and improve code clarity in async callback patterns

Reviewed changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
version.txt	Bumped version from 3.8.0-pre to 4.0.0-pre
CMakeLists.txt	Set CMAKE_CXX_STANDARD to 17 (moved from INTEGRATE_VCPKG block to global scope)
README.md	Added documentation noting C++17 requirement starting from version 4.0.0
pkg/mac/build-static-library.sh	Updated compiler flags from -std=c++11 to -std=c++17
pkg/apk/build-apk.sh	Updated compiler flags from -std=c++11 to -std=c++17
lib/SynchronizedHashMap.h	Replaced boost::optional with std::optional, updated comments and return patterns
lib/ProducerConfigurationImpl.h	Replaced boost::optional with std::optional for member variables
lib/ProducerConfiguration.cc	Replaced boost::make_optional with std::make_optional
lib/ProducerImpl.h	Replaced boost::optional with optional for method parameters and member variables
lib/ProducerImpl.cc	Updated to use std::optional, replaced nullptr with {} for optional initialization
lib/HandlerBase.h	Replaced boost::optional with optional in method signatures
lib/HandlerBase.cc	Adopted weak_from_this() and if-initializers, replaced nullptr with {} for optional
lib/ConsumerImpl.h	Replaced boost::optional with optional in method signatures and member variables
lib/ConsumerImpl.cc	Comprehensive migration to std::optional, adopted weak_from_this() and if-initializers
lib/ConsumerImplBase.cc	Adopted weak_from_this() and if-initializers with static_pointer_cast for proper typing
lib/MultiTopicsConsumerImpl.h	Updated constructor parameters to use optional with default values
lib/MultiTopicsConsumerImpl.cc	Adopted weak_from_this(), changed optional access from get() to value()
lib/Commands.h	Replaced boost::optional with optional in function signatures
lib/Commands.cc	Updated function parameters to use optional, added boost/throw_exception.hpp include
lib/ClientConnection.h	Replaced boost::any with std::any, removed C++14 weak_from_this workaround, replaced boost::optional with optional
lib/ClientConnection.cc	Replaced boost::any_cast with std::any_cast, updated optional value construction
lib/ProducerStatsImpl.cc	Adopted weak_from_this() for cleaner code
lib/ConsumerStatsImpl.cc	Adopted weak_from_this() for cleaner code
lib/UnAckedMessageTrackerEnabled.cc	Adopted weak_from_this() and if-initializers
lib/TableViewImpl.cc	Updated containsKey to use static_cast for optional checking, adopted weak_from_this()
lib/PeriodicTask.cc	Adopted weak_from_this() and if-initializers
lib/NegativeAcksTracker.cc	Adopted weak_from_this() for cleaner code
lib/RetryableOperationCache.h	Adopted weak_from_this() for cleaner code
lib/AckGroupingTrackerEnabled.cc	Adopted weak_from_this() and if-initializers
tests/SynchronizedHashMapTest.cc	Updated tests to use std::optional syntax, removed boost include

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