DNS resolver customization (DoH/DoT/plain), hickory-resolver 0.26 upgrade, and minor fixes

[deedy5]

DNS Resolver Customization

• Adds DohResolver, DotResolver, and PlainDnsResolver backed by hickory-resolver
• Exposes DNS resolver configuration in Python bindings via dns_resolver parameter (string or list of strings for fallback chain)
• Supports doh://, dot://, dns://, and system URL formats
• ChainedResolver tries resolvers in order, returning the first success

Hickory-resolver 0.25 → 0.26 Upgrade

• Fixes NSEC3 closest-encloser proof denial-of-service (unbounded loop)
• Migrates from removed APIs: TokioConnectionProvider → TokioRuntimeProvider, NameServerConfigGroup → Vec<NameServerConfig>, etc.
• Adds system-config feature flag for /etc/resolv.conf support

Fixes & Improvements

• DoH timeout fix: wraps hickory's per-query timeout around DoH lookups to prevent indefinite hangs and enable proper ChainedResolver fallback
• Error messages: includes full error source chain in Python connect/timeout/request exceptions and removes redundant URL tuple argument
• Raw body fix: sends non-object Python values (strings, bytes) as raw request body
• Rustls: removes duplicate "Browser emulation" debug log in ClientHello emission