src_load reads a SEQ file from device 8 once into a bank-1 cache (D118).
It enforces the 80-byte line, 599-line, and 18,999-byte limits as bytes
arrive and reports stable codes with exact positions. src_rewind and
src_next_line replay the cache one logical line at a time for every pass.
diskio.s wraps the KERNAL file calls; channels close on every path.

Verified in x128 with a 1581: eight fixtures, including the exact limits,
each limit error, a missing file (DOS 62), and a missing final $0D, all
match host-computed line counts, Fletcher-16 checksums, and positions.
Adds a shared PowerShell test library for x128 scripts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Add cfg/compiler.cfg, the production mmu.s, c128.inc, and the test mailbox,
proven by a capacity-checking skeleton in x128:

- 8K bottom common RAM, shared code at $1300, private zero page at bank 0
  page $1A via P0, bank-1 tables at $2000-$BFFF, test mailbox at $1BF0
- ld65 rejects overflows of the ZP, COMMON, MAIN, SWSTACK, and TABLES areas
- a CIA #2 timer NMI taken under bank 1 with the private zero page returns
  cleanly through the NMI guard (closes the E01-S03 NMI risk)
- decision D117 records the map; RESTORE is ignored while compiling

Also pin newLang/ to LF in .gitattributes. A branch switch under
core.autocrlf had rewritten the byte-exact fixtures with CRLF.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>