chore(deps): bump libdatadog rev to align with datadog-opentelemetry v0.5.0

Bumps datadog-agent-config's libdd-trace-utils/libdd-trace-obfuscation
git rev from a820699 (8.0.0/4.0.0) to 85ce322a (9.0.0/5.0.0), matching
the exact versions datadog-opentelemetry v0.5.0 already pulls from
crates.io. Combined with a [patch.crates-io] on the consuming side
(datadog-lambda-extension), this collapses the duplicate compiled
copies flagged by Copilot on #144, without switching this crate's
dependency declarations away from git pins (unlike an earlier attempt
that moved to crates.io versions directly - reverted because it broke
type identity for downstream consumers that also depend on these
crates via a git pin, e.g. bottlecap's ReplaceRule usage).

Verified: cargo check/clippy/fmt clean for datadog-agent-config
(default + https features), 79/79 tests pass, dd-rust-license-tool
check passes.

See LIBDATADOG_VERSION_ALIGNMENT.md in datadog-lambda-extension for
full context and the chosen approach (Option A: patch + shared rev
bump) vs alternatives considered.

Author: litianningdatadog