Add MarshalProtoMessage / UnmarshalProtoMessage to grpcstub

[k1LoW]

SSIA

[github-actions]

Code Metrics Report

	main (564153b)	#112 (3bbfbe4)	+/-
Coverage	82.5%	82.8%	+0.3%
Code to Test Ratio	1:0.3	1:0.3	+0.0

Details

  |                    | main (564153b) | #112 (3bbfbe4) |  +/-  |
  |--------------------|----------------|----------------|-------|
+ | Coverage           |          82.5% |          82.8% | +0.3% |
  |   Files            |              3 |              3 |     0 |
  |   Lines            |            664 |            653 |   -11 |
- |   Covered          |            548 |            541 |    -7 |
+ | Code to Test Ratio |          1:0.3 |          1:0.3 |  +0.0 |
  |   Code             |           2682 |           2671 |   -11 |
  |   Test             |            889 |            889 |     0 |

Code coverage of files in pull request scope (82.8% → 83.2%)

Files	Coverage	+/-
grpcstub.go	83.2%	+0.4%

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Reported by octocov