Clarify some of the terminology around energy and activity

[tsmbland]

Description

Pretty much everything that we're currently referring to as "activity" actually refers to an absolute/relative quantity of energy, rather than a rate of energy consumption/production. E.g. whilst the process_availabilities.csv file contains limits on rates of consumption/production in each timeslice, we multiply these by timeslice lengths to get limits on quantities of energy consumption/production. Therefore, a better name for the data structure is EnergyLimitsMap, rather than ActivityLimitsMap. I've changed this, and clarified a few other things.

I think we should use the term "activity" sparingly and only to refer to one specific thing: the maximum PAC production over a year (i.e. the value you get when you multiply capacity by cap2act).

I think the documentation is already specific enough about this, so I haven't changed anything there.

Fixes # (issue)

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.03%. Comparing base (93384c2) to head (51a57ac).
Report is 4 commits behind head on main.

Additional details and impacted files

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  Coverage   95.03%   95.03%           
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  Files          36       36           
  Lines        4914     4914           
  Branches     4914     4914           
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  Hits         4670     4670           
  Misses        123      123           
  Partials      121      121           

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[alexdewar]

A couple of small comments, but otherwise all good 😄

[alexdewar]

I guess this variable name needs changing too?