feat: add r/demo/foo20_lp

[moul]

• adding a fixed-price liquidity pool system for $foo20 <> $GNOT

Depends on #934

Checklists...

Contributors Checklist

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

Maintainers Checklist

• Checked that the author followed the guidelines in CONTRIBUTING.md
• Checked the conventional-commit (especially PR title and verb, presence of BREAKING CHANGE: in the body)
• Ensured that this PR is not a significant change or confirmed that the review/consideration process was appropriate for the change

[r3v4s]

utACK

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (98f384e) 55.93% compared to head (d56798a) 55.94%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #931   +/-   ##
=======================================
  Coverage   55.93%   55.94%           
=======================================
  Files         420      420           
  Lines       65415    65415           
=======================================
+ Hits        36592    36595    +3     
+ Misses      25966    25965    -1     
+ Partials     2857     2855    -2     

see 2 files with indirect coverage changes

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