Impl serde::Serialize and serde::Deserialize for TimeDelta #3481

Job	Run time
alternative_targets (ubuntu-latest, wasm32-unknown-emscripten)	20s
features_check (ubuntu-latest)	3m 54s
alternative_targets (ubuntu-latest, aarch64-apple-ios)	17s
rust_msrv (ubuntu-latest)	1m 55s
rust_versions (ubuntu-latest, stable)	1m 5s
alternative_targets (ubuntu-latest, aarch64-linux-android)	18s
rust_versions (ubuntu-latest, beta)	1m 2s
rust_versions (ubuntu-latest, nightly)	47s
test_wasi (ubuntu-latest, wasm32-wasi)	22s
test_wasm (ubuntu-latest)	30s
timezones (ubuntu-latest, ACST-9:30)	1m 30s
check-docs	21s
timezones (ubuntu-latest, EST4)	1m 35s
timezones (ubuntu-latest, UTC0)	1m 31s
cross-targets (x86_64-unknown-illumos)	1m 6s
timezones (ubuntu-latest, Asia/Katmandu)	1m 26s
timezones (macos-latest, ACST-9:30)	38s
timezones (macos-latest, EST4)	41s
cross-tests (ubuntu-latest)	1m 39s
timezones (macos-latest, UTC0)	44s
timezones (macos-latest, Asia/Katmandu)	38s
timezones (windows-latest, ACST-9:30)	2m 37s
no_std (ubuntu-latest, thumbv6m-none-eabi)	10s
timezones (windows-latest, EST4)	2m 32s
no_std (ubuntu-latest, x86_64-fortanix-unknown-sgx)	17s
timezones (windows-latest, UTC0)	1m 33s
timezones (windows-latest, Asia/Katmandu)	2m 40s
	32m 8s

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