Accommodate `NaN` in `FunctionData` validation and comparison, extend serialization to more types

[GabrielKS]

The market bid cost curve representation relies on putting NaNs in PiecewiseStepData, so I took the opportunity to make ==, isequal, and hash work nicely for FunctionData in general.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 76.94%. Comparing base (d96bb9f) to head (b408a02).

Additional details and impacted files

[](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna) ```diff @@ Coverage Diff @@ ## main #367 +/- ## ========================================== + Coverage 76.86% 76.94% +0.08% ========================================== Files 66 66 Lines 5018 5040 +22 ========================================== + Hits 3857 3878 +21 - Misses 1161 1162 +1 ``` | [Flag](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna) | `76.94% <96.15%> (+0.08%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna) | Coverage Δ | | |---|---|---| | [src/function\_data.jl](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?src=pr&el=tree&filepath=src%2Ffunction_data.jl&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna#diff-c3JjL2Z1bmN0aW9uX2RhdGEuamw=) | `99.31% <100.00%> (+<0.01%)` | :arrow_up: | | [src/serialization.jl](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?src=pr&el=tree&filepath=src%2Fserialization.jl&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna#diff-c3JjL3NlcmlhbGl6YXRpb24uamw=) | `72.72% <ø> (ø)` | | | [src/utils/utils.jl](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?src=pr&el=tree&filepath=src%2Futils%2Futils.jl&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna#diff-c3JjL3V0aWxzL3V0aWxzLmps) | `60.13% <100.00%> (+1.56%)` | :arrow_up: | | [src/hdf5\_time\_series\_storage.jl](https://app.codecov.io/gh/NREL-Sienna/InfrastructureSystems.jl/pull/367?src=pr&el=tree&filepath=src%2Fhdf5_time_series_storage.jl&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NREL-Sienna#diff-c3JjL2hkZjVfdGltZV9zZXJpZXNfc3RvcmFnZS5qbA==) | `96.26% <90.00%> (-0.20%)` | :arrow_down: |