replace panicking unwrap with explicit panic in build.rs

[anaslimem]

What does this PR do?

Resolves a clippy::panicking_unwrap lint error in the Rust build.rs script.

Previously, if compiling the usearch C++ backend failed ( due to missing system headers like <omp.h> on macOS), the build script would unconditionally call .unwrap() on the resulting Err. This caused a generic panic that obscured the actual underlying compiler error and triggered a clippy warning.

Why is this necessary?

Unwrapping an Err value is discouraged by cargo clippy because it leads to unhelpful error messages:

error: this call to `unwrap()` will always panic
   --> build.rs:113:17
    |
...
113 |                 result.unwrap();
    |                 ^^^^^^^^^^^^^^^

This PR replaces the .unwrap() with an explicit panic! that surfaces the exact cxx ToolExecError message. This makes debugging C++ dependency issues during cargo build significantly easier for developers and users.

Testing

Verified locally that:

• cargo clippy --all-targets --all-features passes with zero errors/warnings.
• cargo test -p usearch succeeds with all 14 tests passing.
• Building the crate on a system missing libomp now cleanly displays the fatal error: 'omp.h' file not found message instead of a generic unwrap tracing panic.