Fix GCC 15 -Werror build warnings

[mirounga]

Description

• skip_layer_norm_fusion.cc: make the FindPath matcher paths function-local static const std::vector (they are compile-time constants). Built once instead of per node iteration, and the destructors run at exit rather than inlined into ApplyImpl, sidestepping a -Wfree-nonheap-object false positive.
• test/unittest_util/conversion.h: convert the float<->half / int cast helpers from Eigen Map cast-assignments to std::transform. The Eigen path vectorizes to _mm512_loadu_ps, which GCC 15 mis-flags with -Warray-bounds when inlined into callers passing small fixed-size buffers. Semantics are unchanged.
• zipmap_test.cc: take std::initializer_list and materialize the class-list vector inside TestHelper, keeping the vector out of the inlined TEST body where GCC 15 emits a -Wfree-nonheap-object false positive.

Motivation and Context

GCC 15 with -march=native emits several false-positive warnings that fail the -Werror build. Fixed the underlying code so the warnings no longer fire, with no functional change:

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[mirounga]

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