Add python-numpy-include feature

[robwoolley]

Proposed changes

The b2 python.jam file attempts to import the NumPy module to determine whether the Boost.Python NumPy extension should be enabled. This approach is problematic when cross-compiling, particularly because NumPy includes C extensions built for the target architecture.

Introduce the new python-numpy-include feature to avoid probing for NumPy at build time by allowing the include path to be specified explicitly.

This enables build systems to provide the correct NumPy include directory, eliminating the need to import the NumPy module to find the directory in site-packages.

Sample output of the change when used through BitBake / OpenEmbedded can be seen here: https://lists.openembedded.org/g/openembedded-core/message/243301

Types of changes

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