fix(x/ecocredit): deprecate basket exponent and use precision

[ryanchristo]

Description

Closes: #1133

This pull request deprecates basket exponent and uses credit type precision as exponent for converting credits to basket tokens and for determining the SI prefix used in basket denom.

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #1135 (315e1f5) into master (12969b5) will increase coverage by 5.71%.
The diff coverage is 77.27%.

@@            Coverage Diff             @@
##           master    #1135      +/-   ##
==========================================
+ Coverage   64.12%   69.83%   +5.71%     
==========================================
  Files         215      218       +3     
  Lines       20357    22240    +1883     
==========================================
+ Hits        13053    15531    +2478     
+ Misses       6043     5367     -676     
- Partials     1261     1342      +81     

Flag	Coverage Δ
experimental-codecov	69.68% <77.27%> (?)
stable-codecov	64.15% <77.27%> (+0.03%)	⬆️

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[technicallyty]

lgtm

[aleem1314]

lgtm