Convert a number or boolean argument with asString in four string functions

[youdie006]

matches, normalize-space, substring and string-length switch on the first argument's type with only case string and case query, so a number or boolean falls through and the function works on "". translate, replace, lower-case and concat already convert through asString (func.go:290), which formats numbers and booleans the way string() does. This adds the same default to the four that were missing it.

                          before   after   (translate(12345,'2','x') = "1x345" in both)
string-length(12345)        0        5
string-length(true())       0        4
substring(12345, 2, 3)      ""       "234"
normalize-space(false())    ""       "false"
matches(123, "^123$")       false    true

In practice substring(sum(//price), 1, 3) or string-length(count(//item)) quietly return empty. One behaviour change to call out: matches(1, '^$') was true, because the pattern ran against "", and is now false.

This is the neighbour I mentioned at the end of #141.

Verification

Base 5dbec0f. New cases go into the existing Test_func_string_length, Test_func_substring, Test_func_matches and Test_func_normalize_space.

row	func.go md5	failing
pristine	fce2401a8e2c34dc9e76ec94f464dea0	all four
this PR	79a94deca5d3d6f1599f0b8fdc6f2442	none
fmt.Sprint(typ) instead of asString	87c3659419e6a37b831c39f507e672fc	substring
without the matches default	b773bbd55a438c876eeff698342bbf6a	matches only
without the normalize-space default	458059f925b3e63bf67dbf3dff43cbfc	normalize_space only
without the substring default	bf06ca00efa58bdf901b666a255f3bf0	substring only
without the string-length default	7f63ef27c2c3279677ee70aca266df7f	string_length only

Each partial row fails on its own function alone, so all four sites are needed. The fmt.Sprint row is why substring(1 div 0, 1, 3) is in the table: fmt.Sprint gives +Inf, asString gives Infinity.

testing.yml's go test ./... passes on go1.26.3. coverage.yml's go test -covermode atomic -coverprofile=coverage.out ./... passes on go1.16.15, the version it pins, at 85.3%. go vet ./... clean, gofmt -l empty for both files.

Written with AI assistance (Claude); the measurements above were run locally and I have reviewed the change.

[coveralls]

coverage: 84.221% (+0.04%) from 84.179% — youdie006:scalar-string-args into antchfx:master