Add native dump symbol prefetch and ARM64 triage

[mamoreau-devolutions]

Summary

• add a Rust-native windbg-symbols crate that validates PE/RSDS identities, retrieves exact PE images and PDBs, and reports cache/download provenance
• make dump triage/inspect, daemon dump targets, and address-driven target analysis prefer local images, then acquire exact Microsoft Symbol Server images/PDBs without symsrv.dll or DbgEng srv* paths
• enforce HTTPS Microsoft redirect allowlisting, bounded image downloads, atomic cache writes, identity validation, explicit offline behavior, and forced local DbgEng reloads
• add target-independent ARM64 CONTEXT decoding for x0..x28, fp, lr, sp, pc, and cpsr; ARM64 SYSTEM_SERVICE_EXCEPTION triage now produces a context-driven stack and uses pc for module/symbol evidence
• improve dump triage with typed bugcheck/context/stack limits and driver-evidence qualification; update CLI/MCP/docs/runtime staging accordingly

Validation

• cargo fmt --check
• cargo test -p windbg-symbols
• cargo test -p windbg-dbgeng --lib
• cargo test -p windbg-tool resolves_program_counter
• cargo build -p windbg-tool
• cargo test --workspace
• fresh-cache 0x51 minidump triage downloaded and validated ntoskrnl.exe image key 90B083DA1450000, fetched the matching PDB, and symbolized the registry/pool stack
• fresh-cache 0x3B minidump triage fetched its matching PDB and resolved nt!ExpPoolTrackerChargeEntry+0x40

Notes

• --offline is a hard no-network mode and uses only validated cached artifacts.
• DbgEng is configured exclusively with direct local image/PDB directories; no srv* fallback is introduced.
• The ARM64 decoder is tested against the Windows SDK ARM64_NT_CONTEXT control/integer layout. A real ARM64 dump fixture remains needed for end-to-end runtime validation.