Clean up FeatureMap in API

[qix]

Problem

FeatureMap is part of the API and should be cleaner.

Solution

Cleaned it up a little more, added an optional value type

Result

Just neater, noticed this snuck though. Need to be extra careful about changing the api/ folder

[coveralls]

Pull Request Test Coverage Report for Build 3687868882

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 10 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 61.117%

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Files with Coverage Reduction	New Missed Lines	%
packages/sqrl/src/api/execute.ts	10	42.53%
<!--	Total:	10		-->

Totals
Change from base Build 3681868395:	0.0%
Covered Lines:	15779
Relevant Lines:	24079

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💛 - Coveralls

[meyer]

Just neater, noticed this snuck though. Need to be extra careful about changing the api/ folder

😅 noted