Add systematic type-matrix and fuzz tests for expression functions - #350

test isbool/1 type handling context coercion masks string behavior: "true" via context becomes boolean true (LogicalFunctionsTypeTest)

test rem/2 type handling context-coerced numeric strings work, literal strings raise (NumberFunctionsTypeTest)

test power/2 type handling context-coerced numeric strings work, literal strings raise (NumberFunctionsTypeTest)

test power/2 type handling edge cases: negative base with fractional exponent, huge values (NumberFunctionsTypeTest)

test rem/2 type handling division by zero raises ArithmeticError (NumberFunctionsTypeTest)

test sum/N (sum_vargs) type handling literal strings, booleans, lists and Decimals raise ArithmeticError (NumberFunctionsTypeTest)

test sum/N (sum_vargs) type handling context-coerced numeric strings work (NumberFunctionsTypeTest)

test sum/N (sum_vargs) type handling nil raises ArithmeticError (unlike max/min which tolerate it) (NumberFunctionsTypeTest)

test rem/2 type handling nil raises ArithmeticError (NumberFunctionsTypeTest)

test rem/2 type handling floats, booleans and lists raise ArithmeticError (integers only) (NumberFunctionsTypeTest)

Range.new/2 and first..last default to a step of -1 when last < first. Use Range.new(first, last, -1) or first..last//-1, or pass 1 if that was your intention

missing specification for function from_ucs4be/1

missing specification for function to_ucs4be/1

missing specification for function is_visible_ascii/1

missing specification for function is_visible_latin1/1

missing specification for function is_iso646_basic/1

missing specification for function is_ascii/1

missing specification for function is_latin1/1

missing specification for function is_bmpchar/1

missing specification for function is_unicode/1

missing specification for function is_iso10646/1