Skip serialization of read-only time series

[daniel-thom]

Fixes https://github.com/NREL-SIIP/PowerSystems.jl/issues/711

[codecov[bot]]

Codecov Report

Merging #199 (0b9acb6) into master (f80be08) will decrease coverage by 2.94%. The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
- Coverage   75.16%   72.22%   -2.95%     
==========================================
  Files          42       42              
  Lines        2988     2675     -313     
==========================================
- Hits         2246     1932     -314     
- Misses        742      743       +1     

Flag	Coverage Δ
unittests	72.22% <14.28%> (-2.95%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/hdf5_time_series_storage.jl	94.01% <0.00%> (-0.58%)	:arrow_down:
src/in_memory_time_series_storage.jl	69.14% <0.00%> (-3.13%)	:arrow_down:
src/time_series_storage.jl	72.72% <20.00%> (-16.75%)	:arrow_down:
src/utils/assert_op.jl	44.44% <0.00%> (-13.89%)	:arrow_down:
src/utils/test.jl	42.30% <0.00%> (-7.70%)	:arrow_down:
src/single_time_series.jl	59.74% <0.00%> (-7.29%)	:arrow_down:
src/time_series_container.jl	53.65% <0.00%> (-6.76%)	:arrow_down:
src/serialization.jl	44.44% <0.00%> (-6.06%)	:arrow_down:
src/internal.jl	70.73% <0.00%> (-5.87%)	:arrow_down:
src/utils/utils.jl	55.45% <0.00%> (-4.13%)	:arrow_down:
... and 29 more