Test ContainerIO.calculateSliceOffsetsAndSizes() and fix the slice size calculation

[jmthibault79]

Description

Problem: calculateSliceOffsetsAndSizes() was calculating Slice.size incorrectly.

Impact: Slices created via ContainerIO.readContainer() would produce incorrect sliceByteSize values for their CRAI entries.

Checklist

• [x] Code compiles correctly
• [x] New tests covering changes and new functionality
• [x] All tests passing
• [x] Extended the README / documentation, if necessary
• [ ] Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1326 into master will increase coverage by 0.018%. The diff coverage is 91.304%.

@@               Coverage Diff               @@
##              master     #1326       +/-   ##
===============================================
+ Coverage     67.804%   67.822%   +0.018%     
- Complexity      8252      8253        +1     
===============================================
  Files            562       562               
  Lines          33641     33644        +3     
  Branches        5639      5640        +1     
===============================================
+ Hits           22810     22818        +8     
+ Misses          8658      8654        -4     
+ Partials        2173      2172        -1

Impacted Files	Coverage Δ	Complexity Δ
...va/htsjdk/samtools/cram/structure/ContainerIO.java	62.5% <100%> (+0.772%)	12 <0> (-1)	:arrow_down:
...java/htsjdk/samtools/cram/structure/Container.java	90.476% <90%> (-0.149%)	22 <2> (+2)