fix: validate key characters, throw actionable error

[MichaelGoberling]

Description

• Validate keys against regex, disallow ?, #, /, \
• Throw actionable error

Related Issue

Closes #86

How Has This Been Tested?

Locally linked aio-lib-state in action, npm run test

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #87 (ba1ea80) into master (3b6d45f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #87   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          167       167           
  Branches        33        33           
=========================================
  Hits           167       167           

Impacted Files	Coverage Δ
lib/StateStoreError.js	100.00% <ø> (ø)
lib/StateStore.js	100.00% <100.00%> (ø)

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[moritzraho]

lgtm :)