Enhance CMakeLists for vendored dependency handling

[Bioblaze]

Added support for vendored dependency installation and export rules.

[Copilot]

Pull request overview

This PR enhances the CMakeLists.txt to better support liboai when used as a vendored dependency via add_subdirectory. The changes allow parent projects to provide dependencies as existing targets and control whether install/export rules are generated.

• Added conditional install/export rules that are disabled by default when liboai is not the top-level project
• Modified dependency detection to check for existing targets before calling find_package for both nlohmann_json and CURL
• Made install rules optional via the LIBOAI_INSTALL option

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[Copilot]

The comment says "but if not found, use the vendored target if it exists" which is misleading. The code actually checks if the CURL::libcurl target exists first, and only calls find_package if it doesn't exist. Consider revising to: "Try to use CURL::libcurl target if it exists, otherwise try to find CURL package".

Suggested change

	# Try to find CURL, but if not found, use the vendored target if it exists
	# Try to use CURL::libcurl target if it exists, otherwise try to find CURL package

[Copilot]

The comment says "but if not found, use a target if it exists" which is misleading. The code actually checks if nlohmann_json targets exist first, and only calls find_package if no target exists. Consider revising to: "Try to use nlohmann_json target if it exists, otherwise try to find nlohmann_json package".

Suggested change

	# Try to find nlohmann_json, but if not found, use a target if it exists
	# Try to use nlohmann_json target if it exists, otherwise try to find nlohmann_json package

[Copilot]

For consistency with the nlohmann_json target detection (lines 23-27), consider also checking for a non-namespaced CURL target. Some vendored CURL builds may create a libcurl or curl target without the CURL:: namespace. This would make the dependency detection more robust.

Suggested change

	else()
	find_package(CURL QUIET)
	if(NOT CURL_FOUND)
	message(FATAL_ERROR "CURL not found and CURL::libcurl target does not exist")
	elseif(TARGET libcurl)
	set(CURL_FOUND TRUE)
	add_library(CURL::libcurl ALIAS libcurl)
	elseif(TARGET curl)
	set(CURL_FOUND TRUE)
	add_library(CURL::libcurl ALIAS curl)
	else()
	find_package(CURL QUIET)
	if(NOT CURL_FOUND)
	message(FATAL_ERROR "CURL not found and no suitable libcurl target exists")

[Copilot]

The variable PROJECT_IS_TOP_LEVEL is only available in CMake 3.21 and later, but this file requires CMake 3.13 (line 1). This will cause a build failure on CMake versions between 3.13 and 3.20. Either update the minimum required version to 3.21, or add a check to define PROJECT_IS_TOP_LEVEL for older versions.