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/os/os.ww

@@ -119,9 +119,11 @@ export fn filesize(fd: i32) i64 = {
 	return end;
 };
 
-// readfull — keep reading until `n` bytes have arrived or the fd
+// readall — keep reading until `n` bytes have arrived or the fd
 // closes early. Returns bytes read (0..=n) or -1 on read error.
-export fn readfull(fd: i32, buf: *u8, n: u64) i64 = {
+// Hare name (io::readall); the buffer is caller-supplied, matching
+// the Plan 9 subset convention.
+export fn readall(fd: i32, buf: *u8, n: u64) i64 = {
 	let got: u64 = 0u64;
 	for (got < n) {
 		let r: i64 = read(fd, buf + got, n - got);
@@ -132,9 +134,10 @@ export fn readfull(fd: i32, buf: *u8, n: u64) i64 = {
 	return got: i64;
 };
 
-// writefull — keep writing until `n` bytes have been accepted or the
-// fd refuses progress. Returns bytes written or -1.
-export fn writefull(fd: i32, buf: *u8, n: u64) i64 = {
+// writeall — keep writing until `n` bytes have been accepted or the
+// fd refuses progress. Returns bytes written or -1. Hare name
+// (io::writeall).
+export fn writeall(fd: i32, buf: *u8, n: u64) i64 = {
 	let sent: u64 = 0u64;
 	for (sent < n) {
 		let r: i64 = write(fd, buf + sent, n - sent);
@@ -153,8 +156,8 @@ export fn access(path: *u8, mode: i32) i32 = {
 	return syscall2(SYS_ACCESS, path: i64, mode: i64): i32;
 };
 
-// unlink(2).
-export fn unlink(path: *u8) i32 = {
+// remove — unlink(2). Hare name; the underlying syscall is unlink(2).
+export fn remove(path: *u8) i32 = {
 	return syscall1(SYS_UNLINK, path: i64): i32;
 };