fix: Patch coarsetime for MIPS AtomicU64 support

- Vendor coarsetime crate with portable-atomic fallback
- Use portable-atomic on targets without 64-bit atomics
- Patch crates.io to use local coarsetime
- Fixes MIPS build failure (AtomicU64 missing)

third_party/coarsetime/LICENSE

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+BSD 2-Clause License
+
+Copyright (c) 2016-2026, Frank Denis
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