#1399: preserve large PMP integers

[gemshrine]

Fixes #1399.

Fbe.pmp used to pass every int setting through Float to check for a fractional part. Float cannot represent every integer above 2^53, so reading a valid setting could silently change it.

Integer inputs now bypass Float conversion, and integer strings are parsed directly. Other numeric inputs still use the whole-number validation. The regression test uses 9_007_199_254_740_993 in the hr.anger setting and checks that the exact value is returned.

test/fbe/test_pmp.rb covers the regression. CI runs the project checks.