Refactor: Optimize SYCL element-wise operations with unary function inlining

This commit refactors the SYCL element-wise operations to improve performance by:

- Inlining unary operations (sgn, abs, elu, gelu, silu, etc.) to reduce kernel launch overhead.
- Introducing helper functions `op_xxx` for each unary operation to encapsulate the logic.
- Replacing direct kernel calls with calls to these inlined functions.
- Using `__dpct_inline__` to encourage compiler inlining.
- Minor code cleanup and consistency improvements.

The changes aim to reduce kernel launch overhead and improve the overall efficiency of element-wise operations on SYCL devices.

Author: qnixsynapse