Expand coverage for Epoch Unit tests

[BrandonWeng]

Describe your changes and provide context

• expand keeper, simulation coverage to 100%,
• types only covered the important parts, most of it is auto-generated code
• epoch module has a lot of builder plate per module

Testing performed to validate your change

Before

> go test -coverprofile=coverage.out ./x/epoch/...
ok      github.com/sei-protocol/sei-chain/x/epoch       0.349s  coverage: 13.8% of statements
?       github.com/sei-protocol/sei-chain/x/epoch/client/cli    [no test files]
?       github.com/sei-protocol/sei-chain/x/epoch/client/wasm   [no test files]
?       github.com/sei-protocol/sei-chain/x/epoch/client/wasm/bindings  [no test files]
ok      github.com/sei-protocol/sei-chain/x/epoch/keeper        0.618s  coverage: 65.5% of statements
?       github.com/sei-protocol/sei-chain/x/epoch/simulation    [no test files]
ok      github.com/sei-protocol/sei-chain/x/epoch/types 0.249s  coverage: 1.6% of statements

After

ok      github.com/sei-protocol/sei-chain/x/epoch       0.726s  coverage: 76.8% of statements
?       github.com/sei-protocol/sei-chain/x/epoch/client/cli    [no test files]
?       github.com/sei-protocol/sei-chain/x/epoch/client/wasm   [no test files]
?       github.com/sei-protocol/sei-chain/x/epoch/client/wasm/bindings  [no test files]
ok      github.com/sei-protocol/sei-chain/x/epoch/keeper        0.440s  coverage: 100.0% of statements
ok      github.com/sei-protocol/sei-chain/x/epoch/simulation    0.312s  coverage: 100.0% of statements
ok      github.com/sei-protocol/sei-chain/x/epoch/types 0.477s  coverage: 1.9% of statements

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@a82ed66). Click here to learn what that means.
Patch has no changes to coverable lines.

❗ Current head b47adbe differs from pull request most recent head de29c8c. Consider uploading reports for the commit de29c8c to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #849   +/-   ##
=========================================
  Coverage          ?   19.25%           
=========================================
  Files             ?      291           
  Lines             ?    53444           
  Branches          ?        0           
=========================================
  Hits              ?    10288           
  Misses            ?    42571           
  Partials          ?      585           

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