[WebGPU] Fix nearest half-tie handling for round_prefer_ceil/floor

[haoxli]

Description

ResizeOpTest.ResizeOpNearestUpSample_RoundPreferCeil_HalfPixel_2x2to7x8 fails on Intel WebGPU devices:

error: The difference between cur_expected[i] and cur_actual[i] is 2, which exceeds tolerance, where
cur_expected[i] evaluates to 3,
cur_actual[i] evaluates to 1, and
tolerance evaluates to 0.00030999997397884727.

Motivation and Context

The WebGPU shader logic used exact half-tie equality checks combined with i32 truncation arithmetic. This approach is fragile under GPU floating-point precision constraints and misbehaves on negative halfway coordinates.

This change replaces the exact comparisons with a robust, epsilon-based fractional tie check (<= 1e-6) for both ROUND_PREFER_CEIL and ROUND_PREFER_FLOOR execution paths.

Also add regression coverage for round_prefer_floor in resize_op_test.cc:

• ResizeOpNearestUpSample_RoundPreferFloor_HalfPixel_2x2to7x8
• ResizeOpNearestUpSample_RoundPreferFloor_HalfPixel_GH28291_Regression

[haoxli]

CI failure due to OOM:

1: AddressSanitizer: Out of memory. The process has exhausted 8192MB for size class 8192.
1: =================================================================
1: ==18400==ERROR: AddressSanitizer: allocator is out of memory trying to allocate 0x2000 bytes
1: AddressSanitizer: nested bug in the same thread, aborting.

3/4 Test #1: onnxruntime_test_all .............***Failed  1307.52 sec
Debug (cpuinfo): HTT: APIC ID = 00000018, cores per processor = 32
Debug (cpuinfo): raw CPUID brand string: " AMD EPYC 9V74 80-Core Processor                "
Debug (cpuinfo): detected 1 processor groups
Debug (cpuinfo): detected 32 processors in group 0
Debug (cpuinfo): detected 0 processors before group 0
Debug (cpuinfo): reconstructed APIC ID 0x00000000 for processor 0 in group 0