Move known_callables from ASTBuilderBase to TargetBase (split into host/device variants)

[Copilot]

• Add known_callables property to TargetBase returning {}
• Update ASTBuilderBase.known_callables to delegate to self.target.known_device_callables
• Add known_callables override to DummyHostASTBuilder delegating to self.target.known_host_callables
• Add known_callables override to PythonASTBuilderBase delegating to self.target.known_host_callables
• Move CFamilyASTBuilder.known_callables → CFamilyTarget.known_device_callables
• Move CUDACASTBuilder.known_callables → CudaTarget.known_device_callables
• Move OpenCLCASTBuilder.known_callables → OpenCLTarget.known_device_callables
• Move PyOpenCLCASTBuilder.known_callables → PyOpenCLTarget.known_device_callables; add PyOpenCLTarget.known_host_callables returning C callables for Python host builder
• Move CWithGNULibcASTBuilder.known_callables → CWithGNULibcTarget.known_device_callables
• Fix ExecutableCWithGNULibcTarget to also override known_device_callables with GNU libc callables (fixes test_glibc_bessel_functions)
• Update translation_unit.py to use t_unit.target.known_device_callables
• Update tools.py to use self.target.known_device_callables
• Update library/reduction.py to use target.known_device_callables["max/min"]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Move known_callables into TargetBase, from ASTBuilder</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Move known_callables into TargetBase, from ASTBuilder #988

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[inducer]

@copilot Note that there should be two versions of known_callables on the target, one for host code, and another for device code.

[Copilot]

@copilot Note that there should be two versions of known_callables on the target, one for host code, and another for device code.

Done in 91bbd26. TargetBase now has both known_host_callables and known_device_callables (each returning {} by default).

• ASTBuilderBase.known_callables delegates to target.known_device_callables (device is the default)
• DummyHostASTBuilder.known_callables and PythonASTBuilderBase.known_callables delegate to target.known_host_callables
• PyOpenCLTarget overrides known_host_callables to return C callables (for the Python host builder)
• All target subclasses now override known_device_callables instead of a single known_callables

[inducer]

@copilot Why does test_glibc_bessel_functions fail with these changes?

[Copilot]

@copilot Why does test_glibc_bessel_functions fail with these changes?

ExecutableCWithGNULibcTarget extends ExecutableCTarget (not CWithGNULibcTarget), so it didn't inherit the known_device_callables override that adds get_gnu_libc_callables(). Previously this worked because both shared the same CWithGNULibcASTBuilder device builder that had the callables. Fixed in 844de53 by adding the known_device_callables override to ExecutableCWithGNULibcTarget as well.