fix(deps): bump crossbeam-epoch to 0.9.20

[jdrouet]

Bumps crossbeam-epoch from 0.9.18 to 0.9.20 in Cargo.lock.

Why

The security audit job is failing on RUSTSEC-2026-0204 — invalid pointer dereference in the fmt::Pointer impl for Atomic and Shared when the underlying pointer is invalid. Patched in >= 0.9.20.

crossbeam-epoch is pulled in transitively via crossbeam-deque, so the advisory fails the audit job on main and on every dependency PR — that is what is currently blocking #659, which is otherwise unrelated to this crate.

Lockfile-only change: cargo update -p crossbeam-epoch.

Verification

• cargo build --workspace --all-features — passes
• cargo test --workspace --all-features — passes

[jdrouet-datadog-monitor]

⚠️ Warnings

🚦 1 Pipeline job failed

security audit | security_audit     

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[jdrouet]

Merging with security_audit red on purpose. The audit reports one advisory at a time, and there are currently two outstanding:

• RUSTSEC-2026-0204 crossbeam-epoch — fixed by this PR
• RUSTSEC-2026-0185 quinn-proto (CVE-2026-25800, remote memory exhaustion) — fixed by build(deps): Bump quinn-proto from 0.11.14 to 0.11.16 #659

So neither PR can be green on its own: before this change the audit stopped at crossbeam-epoch, and with it applied the audit gets one step further and stops at quinn-proto. Landing this and then #659 leaves main audit-clean. security_audit is not a required check, and every other check here passes.