lib: rename stdlib surface to Hare names; add endian/math

Sweeping rename so the lib/ surface mirrors Hare's stdlib spellings.
- ascii: rune-taking predicates; ishex -> isxdigit
- bufio: rinit -> init; take1/takeline -> readbyte/readline
- bytes: indexsub -> index
- encoding/utf8: runelen -> runesz
- errors: eEOF/eShortRead/... -> eof/underread/...
- fmt: errln -> errorln; println/fprintln return i64
- os: readfull/writefull -> readall/writeall; unlink -> remove
- path: isabs -> abs; drop lastindex (now strings.rbyteindex)
- strconv: u64toa/i64toa -> u64tos/i64tos; parse64/parseu64 -> stoi64/stou64
- strings: drop len/isempty; equal -> compare; indexbyte -> byteindex; +rbyteindex
- types: drop numeric helpers (moved to math)
- new lib/endian (htonu16/ntohu16), lib/math (absi32/absi64)
- net: drop htons (use endian.htonu16)

Callers in selfhost/, lib/ww/, cmd/w6c/cgen.c, and test/wcc/700_e2e.c
updated to match.

lib/path/path.ww

@@ -1,15 +1,8 @@
 // path — filesystem path manipulation. UTF-8 paths, '/' separator.
+// Mirrors Hare's path:: surface. Reverse byte search lives in strings
+// (strings::rbyteindex), not here.
 
-export fn isabs(p: str) bool = {
+export fn abs(p: str) bool = {
 	if (p.len == 0) { return false; };
 	return p[0] == ('/': u8);
 };
-
-export fn lastindex(p: str, c: u8) i32 = {
-	let i: i32 = p.len - 1;
-	for (i >= 0) {
-		if (p[i] == c) { return i; };
-		i -= 1;
-	};
-	return -1;
-};