Switch CCF builds to C++23

[Amaury Chamayou (achamayou)]

• require C++23 for CCF builds via CMAKE_CXX_STANDARD in preproject.cmake, which reaches downstream consumers through ccf-config.cmake
• update the installed-application smoke test to fall back to Clang 18, matching the packaged minimum toolchain
• fix C++23 compatibility issues in the vendored SmallVector include sites (std::aligned_union is deprecated by P1413R3) and incomplete pimpl declarations
• adopt C++23 std::to_underlying, string and ranges contains, and std::unreachable, and remove the obsolete comparison shim

[Copilot]

Pull request overview

This PR updates CCF’s build and public CMake targets to require C++23, and modernises several call sites to use C++23 standard library APIs (eg std::to_underlying, std::ranges::contains, std::string{,_view}::contains, std::unreachable) while keeping tests and vendored include sites compatible.

Changes:

• Switch default CMake C++ standard to 23 and propagate cxx_std_23 via exported/linked targets.
• Update the install-build smoke test to fall back to Clang 18.
• Replace legacy shims/patterns with C++23 equivalents (string/ranges contains, std::to_underlying, std::unreachable) and adjust a few includes/headers accordingly.

Custom instructions used:

• None (no additional .github/copilot-instructions.md / .github/instructions/* files were loaded via tools in this review).

Reviewed changes

Copilot reviewed 43 out of 43 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_install_build.sh	Update compiler fallback to clang/clang++ 18 for install-build smoke test.
src/tasks/worker.cpp	Use std::unreachable() (and include <utility>).
src/tasks/test/basic_tasks.cpp	Use std::string::contains in task tests.
src/tasks/ordered_tasks.h	Remove redundant = nullptr from unique_ptr pimpl member.
src/tasks/job_board.h	Remove redundant = nullptr from unique_ptr pimpl member.
src/tasks/fan_in_tasks.h	Remove redundant = nullptr from unique_ptr pimpl member.
src/node/test/js_policy.cpp	Use std::string::contains in policy error-handling tests.
src/node/test/historical_queries.cpp	Replace std::find with std::ranges::contains in historical query tests.
src/node/rpc/test/frontend_test.cpp	Use std::string::contains in RPC frontend tests.
src/node/rpc/test/frontend_test_infra.h	Use std::string::contains in shared test helper.
src/node/rpc/node_frontend_utils.h	Use std::to_underlying for enum formatting in error path (include <utility>).
src/node/rpc/file_serving_handlers.h	Use std::string::contains when parsing range headers.
src/node/node_state.h	Use std::string_view::contains in hostname/IP detection.
src/node/node_inbound_message.h	Use std::to_underlying for enum formatting in error path (include <utility>).
src/kv/untyped_map.h	Remove obsolete operator!= shim now that C++23 is required.
src/kv/test/kv_test.cpp	Use std::string::contains in KV unit tests.
src/kv/raw_serialise.h	Wrap vendored SmallVector include with deprecation-warning suppression pragmas.
src/js/test/js.cpp	Use std::string::contains in JS KV map access test helper.
src/js/extensions/ccf/kv_helpers.h	Remove outdated comment about std::to_underlying.
src/http/test/http_test.cpp	Add <algorithm> and use contains / std::ranges::contains in HTTP tests.
src/http/http2_parser.h	Use std::to_underlying for HTTP status formatting (include <utility>).
src/host/test/ledger.cpp	Use std::string::contains for ledger filename checks.
src/ds/test/messaging.cpp	Use std::string::contains in exception message assertions.
src/ds/test/logger.cpp	Use std::string::contains in logger output assertions.
src/ds/test/json_schema.cpp	Add <algorithm> and use std::ranges::contains in schema tests.
src/crypto/test/crypto.cpp	Use std::string::contains in certificate validity assertions.
src/crypto/pem.cpp	Use std::string::contains in PEM format validation.
src/cose/test/cose_ffi_test.cpp	Use std::string::contains in COSE error assertions.
src/consensus/aft/test/committable_suffix.cpp	Add <algorithm> and use std::ranges::contains in AFT test helper.
src/common/cli_helper.h	Use std::string::contains for IPv6 bracket validation.
include/ccf/tx_status.h	Use std::to_underlying in FinalTxStatus and include <utility>.
include/ccf/service/tables/proposals.h	Use std::to_underlying for proposal-state formatting and include <utility>.
include/ccf/service/node_info_network.h	Use std::string::contains in address parsing/formatting helpers.
include/ccf/js/kv_access_permissions.h	Implement permission intersection via std::to_underlying (include <utility>).
include/ccf/endpoint.h	Use std::to_underlying in forwarding-required formatter.
include/ccf/ds/logger.h	Use std::to_underlying for logger level indexing (include <utility>).
include/ccf/ds/hash.h	Wrap vendored SmallVector include with deprecation-warning suppression pragmas.
include/ccf/ds/enum_formatter.h	Use std::to_underlying in generic enum formatter (include <utility>).
include/ccf/byte_vector.h	Wrap vendored SmallVector include with deprecation-warning suppression pragmas.
cmake/preproject.cmake	Set CMAKE_CXX_STANDARD to 23 and require it.
cmake/crypto.cmake	Propagate cxx_std_23 on ccfcrypto target.
cmake/ccf_app.cmake	Apply/propagate cxx_std_23 on app and static library helper targets.
CHANGELOG.md	Document the C++23 requirement and exported-target propagation (#8234).

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