mrc-4455 Support multiple varying parameters in batches

[EmmaLRussell]

Adds support for multiple varying parameters in the running of sensitivity. For consistency, running single parameter sensitivity is now done in the same way, with just a single varying parameter defined.

Key changes:

• in BatchPars, the name and values props have been replaced by an array of VaryingPars (each of which has a parameter name and array of values).
• expandVaryingParams method is used to generate all combinations of varying params values (as an array of UserTypes) - batchRun iterates through this array and computes for each of these combinations
• BatchError has been replaced by RunStatus which is recorded for each combination of varying parameter values and includes success boolean. the varying parameter values and any error strings.
• Two getters give useful access to the run statuses, the first returning errors only, and the second returning the successful parameter value combinations, which will correspond by index to the returned solutions list
• the summary series sets which previously had the single varying parameter's values as its x values, now needs to specify the multiple varying parameter values, so there's now a UserTypeSeriesSet type where x is an array of UserTypes specifying these multiple values. (Maybe x isn't a sensible name for this any more!)

[codecov]

Codecov Report

Patch coverage is 100.00% of modified lines.

Files Changed	Coverage
src/solution.ts	ø
src/versions.ts	ø
src/batch.ts	100.00%

📢 Thoughts on this report? Let us know!.

[richfitz]

This is great, and less disruptive than expected. One suggestion about making the expansion part more resable.

[richfitz]

oh did we make this already non blocking? that was good of us

[richfitz]

this could be a free function rather than a method, and then would be easier to put a few unit tests on. I'd not be surprised if we use this elsewhere (in this project or adapt to another) so might be worthwhile.