Printing floating-point values in `hexfloat` results in exponential format

[fbarbari]

Describe the bug

When printing floating-point values with the hexfloat formatting through a sycl::stream from inside a SYCL kernel, the actual formatting being applied is the same as sycl::scientific.

To reproduce

Compiler Explorer reproducer

Environment

• OS: RHEL 8.8
• Target device and vendor: Intel Xeon Platinum 8358
• DPC++ version: any version >= 2025.0.0
• Dependencies version: output of sycl-ls --verbose

[opencl:cpu][opencl:0] Intel(R) OpenCL, Intel(R) Xeon(R) Platinum 8358 CPU @ 2.60GHz OpenCL 3.0 (Build 0) [2025.19.4.0.18_160000.xmain-hotfix]

Platforms: 1
Platform [#1]:
    Version  : OpenCL 3.0 LINUX
    Name     : Intel(R) OpenCL
    Vendor   : Intel(R) Corporation
    Devices  : 1
        Device [#0]:
        Type              : cpu
        Version           : OpenCL 3.0 (Build 0)
        Name              : Intel(R) Xeon(R) Platinum 8358 CPU @ 2.60GHz
        Vendor            : Intel(R) Corporation
        Driver            : 2025.19.4.0.18_160000.xmain-hotfix
        UUID              : 13412816666025525125412725525123519100
        DeviceID          : UNKNOWN
        Num SubDevices    : 2
        Num SubSubDevices : 0
        Aspects           : cpu fp16 fp64 online_compiler online_linker queue_profiling usm_device_allocations usm_host_allocations usm_shared_allocations usm_system_allocations usm_atomic_host_allocations usm_atomic_shared_allocations atomic64 ext_intel_device_info_uuid ext_oneapi_srgb ext_oneapi_native_assert ext_intel_legacy_image ext_oneapi_ballot_group ext_oneapi_fixed_size_group ext_oneapi_opportunistic_group ext_oneapi_tangle_group ext_oneapi_private_alloca ext_oneapi_atomic16 ext_oneapi_virtual_functions
        info::device::sub_group_sizes: 4 8 16 32 64
        Architecture: x86_64

Additional context

No response