Added length function to Month so that I don't have to use time crate #3523

Job	Run time
check-docs	22s
cross-tests (ubuntu-latest)	1m 50s
cross-targets (x86_64-unknown-illumos)	1m 30s
alternative_targets (ubuntu-latest, wasm32-unknown-emscripten)	15s
features_check (ubuntu-latest)	3m 47s
alternative_targets (ubuntu-latest, aarch64-apple-ios)	19s
no_std (ubuntu-latest, thumbv6m-none-eabi)	13s
rust_msrv (ubuntu-latest)	1m 50s
alternative_targets (ubuntu-latest, aarch64-linux-android)	13s
no_std (ubuntu-latest, x86_64-fortanix-unknown-sgx)	15s
rust_versions (ubuntu-latest, stable)	1m 6s
test_wasi (ubuntu-latest, wasm32-wasi)	31s
rust_versions (ubuntu-latest, beta)	1m 14s
test_wasm (ubuntu-latest)	53s
rust_versions (ubuntu-latest, nightly)	1m 2s
timezones (ubuntu-latest, ACST-9:30)	1m 23s
timezones (ubuntu-latest, EST4)	1m 28s
timezones (ubuntu-latest, UTC0)	1m 22s
timezones (ubuntu-latest, Asia/Katmandu)	1m 12s
timezones (macos-latest, ACST-9:30)	46s
timezones (macos-latest, EST4)	44s
timezones (macos-latest, UTC0)	45s
timezones (macos-latest, Asia/Katmandu)	46s
timezones (windows-latest, ACST-9:30)	2m 24s
timezones (windows-latest, EST4)	3m 28s
timezones (windows-latest, UTC0)	2m 19s
timezones (windows-latest, Asia/Katmandu)	1m 54s
	33m 51s

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