chore: add new oracle period

[apopiak]

This PR adds a new oracle period with a = 0.2 (which corresponds to a 9 block oracle when calculating with smoothing_from_period).

Based on #182

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03 🎉

Comparison is base (9958aa7) 73.38% compared to head (24be51d) 73.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
+ Coverage   73.38%   73.42%   +0.03%     
==========================================
  Files          41       41              
  Lines        3438     3443       +5     
==========================================
+ Hits         2523     2528       +5     
  Misses        915      915              

Impacted Files	Coverage Δ
ema-oracle/src/benchmarking.rs	98.77% <100.00%> (+0.03%)	⬆️
ema-oracle/src/types.rs	81.94% <100.00%> (+0.25%)	⬆️

... and 1 file with indirect coverage changes

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[enthusiastmartin]

the benchmarking changes are part of another PR.