Add test coverage for RequestMapper and DecisionMapper

[natemort]

What changed?

• Add Tests for converting thrift requests to proto requests.
• Add tests for converting thrift Decisions to proto Decisions

Why?

• Increasing code coverage and discovering bugs

How did you test it?

• Running the unit tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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[coveralls]

Pull Request Test Coverage Report for Build 2536

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+3.3%) to 65.287%

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Files with Coverage Reduction	New Missed Lines	%
src/main/java/com/uber/cadence/internal/replay/ReplayDecisionTaskHandler.java	1	87.8%
src/main/java/com/uber/cadence/internal/testservice/TestWorkflowMutableStateImpl.java	1	83.5%
src/main/java/com/uber/cadence/internal/replay/ReplayDecider.java	5	80.27%

Totals
Change from base Build 2526:	3.3%
Covered Lines:	12733
Relevant Lines:	19503

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💛 - Coveralls