Reconfigure usage of technology modules in tools.costs

[measrainsey]

Change the implementation of technology modules (e.g., "energy", "materials") to be more agnostic to module name

In preparation of adding a module for cooling technologies, I have reconfigured the tools.costs code base to be more agnostic to the module name being specified.

The main changes are:

• Remove the module name from the CSV file names (redundant since the folders are already the module name)
• Incorporate first_year.csv into tech_map.csv to remove the necessity of the first_year.csv file
• Transition to using an agnostic module name instead of materials when possible

Because the materials module still requires an additional Intratec dataset, there are still instances where the specific materials module needs to be explicitly mentioned.

This PR's branch is derived from the costs/new-inputs branch, which is under review in the PR #206. Once that PR is approved and merged, I will rebase this branch onto main.

How to review

For @khaeru and/or @glatterf42 : Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Update doc/whatsnew.

[glatterf42]

Looks good to me, approved assuming the tests pass after the announced rebase :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.5%. Comparing base (4d8ec92) to head (df31a55).
Report is 14 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #221     +/-   ##
=======================================
- Coverage   66.5%   65.5%   -1.0%     
=======================================
  Files        204     204             
  Lines      15822   15823      +1     
=======================================
- Hits       10526   10379    -147     
- Misses      5296    5444    +148     

Files with missing lines	Coverage Δ
message_ix_models/tools/costs/decay.py	100.0% <100.0%> (ø)
..._ix_models/tools/costs/regional_differentiation.py	97.9% <100.0%> (+<0.1%)	⬆️

... and 7 files with indirect coverage changes