[fix] Extract dependencies from object reference instead of class

[katyho]

Summary

From here, the object reference is used to call the dependency block, not the class. Fix extracting dependencies when calling dependency_of to use the object reference as well.

Usually we have something like

memoize_method :method |_, *args| do...
end

so we don't care about the first argument.

Testing

Added specs to cover scenario. Without this change, the specs fail with something like

     Failure/Error: depends_on RedisMemo::Memoizable.new(id: obj.id, val: x)

     NoMethodError:
       undefined method `id' for #<Class:0x000056241936d420>

Specs succeed with this change

[codecov-io]

Codecov Report

Merging #13 (090a2e2) into main (cc19d07) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   96.62%   96.63%           
=======================================
  Files          30       30           
  Lines        1691     1693    +2     
=======================================
+ Hits         1634     1636    +2     
  Misses         57       57           

Impacted Files	Coverage Δ
lib/redis_memo/memoize_method.rb	96.42% <100.00%> (-0.13%)	⬇️
spec/memoizable/dependency_spec.rb	99.30% <100.00%> (+0.02%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cc19d07...090a2e2. Read the comment docs.

[donaldong]

maybe we should prefix this instance var with redis_memo to avoid potential conflicts?