perf: cache CryptoProvider/RootCertStore/BrowserEmulator, optimize Python iterators, fix Random OS consistency

[deedy5]

Summary:

1. 81f4e35 — perf: cache TLS config, eliminate recursion

• Cache CryptoProvider and RootCertStore in OnceLock to avoid repeated lookups and allocations
• Cache BrowserEmulator in Arc via OnceLock across all browsers (Chrome, Edge, Firefox, Opera, Safari) — avoids cloning TLS fingerprint vectors on every request
• Eliminate recursion in os_platform() and Safari's build_user_agent() by resolving Random upfront
• Set os_type on Safari BrowserEmulator via Arc::make_mut

2. b75c8fd — perf: optimize Python iterators, reduce clones

• Cache encoding lookup per-iterator (&'static Encoding) instead of per-chunk in TextIterator/AsyncTextIterator
• Pre-allocate buffers with Vec::with_capacity()
• Change LinesIterator/AsyncLinesIterator buffer from String to Vec — avoids UTF-8 conversion on every chunk, only converts on line extraction
• Move redirect policy restoration before async block (reduces lock-hold window)
• Eliminate headers.clone() in all Python HTTP method helpers (pass ownership)

3. 58215c5 — fix: consistent Random OS resolution

• Resolve ImpersonateOS::Random once per build_*_settings call instead of independently at each consumer (User-Agent, sec-ch-ua-mobile, sec-ch-ua-platform, Safari TLS os_type), preventing header inconsistencies