Stub out a components test, and use serde serialization for DateTime options

[gregtatum]

This PR stubs out a single test for components. In order to do that, I opted for using serde serialization, as an optional dependency. I took the Cargo.toml approach from #451.

I went ahead, and in this PR, converted over the Style bag's tests to use serde serialization as well.

[gregtatum]

Looks like I still have a few CI failures on the features job. I'll take a look at that on Monday.

[coveralls]

Pull Request Test Coverage Report for Build eeb56620c66f56c7d60a0e6f44e53e354be61eef-PR-461

• 0 of 3 (0.0%) changed or added relevant lines in 3 files are covered.
• 22 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.3%) to 73.147%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
components/datetime/src/options/components.rs	0	1	0.0%
components/datetime/src/options/preferences.rs	0	1	0.0%
components/datetime/src/options/style.rs	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
components/datetime/src/fields/symbols.rs	1	76.29%
components/datetime/src/options/components.rs	1	16.67%
components/datetime/src/options/style.rs	1	33.33%
components/datetime/src/format.rs	8	72.41%
components/datetime/src/provider/helpers.rs	11	57.29%

Totals
Change from base Build ae89da479dfbbcfc73fbaa977cd3f4ecfd0e4fac:	-0.3%
Covered Lines:	4737
Relevant Lines:	6476

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💛 - Coveralls

[gregtatum]

I fixed the issue on the build. Since serde is an optional dependency, it might not exist. The conditional is now a bit gross, but it turns into a check for not having the serialize_none feature AND having the serde feature.