[FEATURE]: Add ugrep search engine backend for multi-core single-file performance

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Describe the enhancement you want to request

Problem

ripgrep (rg) runs single-threaded when searching individual large files (logs, bundles, datasets) and slows down on PCRE2 lookaround patterns (rg -P).

Solution

Support ugrep as a search backend.

Key Advantages

In my Ubuntu 24.04 ARM64 system:
• 15.7x Faster Single-File Matches: ugrep splits single files across CPU cores via mmap chunking.
• 30.3x Faster Case-Insensitive Search (-i): Hardware SIMD bit-parallel case-folding (ARM NEON / AVX-512).
• 300x Faster PCRE2 Lookarounds (-P): SIMD pre-filtering before PCRE2 JIT execution.

Proposed Action

Add a configurable search binary path (--search-engine=ugrep or UGREP_PATH) with automatic fallback to rg.