Add inline comments for unused variables

[trmid]

Improves code readability and intention. Example:

function foo(address) external;

vs.

function foo(address /* user */) external;

[linear]

GEN-1217 QA-237 [N-37]

[github-actions]

LCOV of commit 611404a during coverage #488

Summary coverage rate:
  lines......: 99.0% (202 of 204 lines)
  functions..: 100.0% (55 of 55 functions)
  branches...: no data found

Files changed coverage rate:
                              |Lines       |Functions  |Branches    
  Filename                    |Rate     Num|Rate    Num|Rate     Num
  ==================================================================
  src/PrizeVault.sol          |98.9%    174| 100%    44|    -      0