Murisi/settable native precision

[murisi]

Describe your changes

Based on #4510. The normed inflation is currently (in main) stored in the ConversionState structure in memory. This is potentially problematic because it means that neither governance upgrades nor storage key-based hard fork migrations can change this value. This PR addresses this potential issue by:

1. moving the normed inflation value into the native token's precision key. (The value was moved to this key because it's used in exactly the same way as precisions for non-native tokens: to control the precision of the inflation computation and as the threshold for rewards.)
2. moving the reference inflation value from the token precision key (which, because of (1), now stores the current native precision) to a new key called the MASP base native precision storage key.
3. introducing a new key to allow scheduled changes to the base native precision key. Just like in Scheduled conversion and precision migrations #4510, this will allow migrations targetting the base native precision key to be applied without knowing the MASP epoch in which they will be applied.

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (6154e11) to head (e6d957f).
Report is 52 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff      @@
##   main   #4522   +/-   ##
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