as65: implement -n properly (currently an accepted no-op)

[relmer]

-n is accepted by CassoCli in as65 mode and does nothing. It is parsed, stored
in disableOpt, copied into AssemblerOptions, and read by no code.

In real as65 it is not a no-op:

-n — "Disable optimizations. When this option is specified no
optimizations will be done, even when the OPT pseudo-instruction is used."

Source: as65 1.42 manual, https://raw.githubusercontent.com/Ludoclt/as65_142/master/as65.man

So it has to override OPT, not merely skip a default.

The optimization it has to disable

Operand mode selection picks zero page when the address fits — AssemblySession.cpp,
the expr candidate list, "a branch target, a jump target, then zero page if it
fits". Nothing there consults disableOpt.

Measured on the built binary:

        ORG $6000
        LDA $0010
        RTS

	bytes
without -n	A5 10 60 — zero page
with -n	A5 10 60 — identical

Acceptance

• -n suppresses the zero-page selection, so LDA $0010 assembles to AD 10 00.
• It does so even where OPT asks for optimization.
• Covered by a test that fails when the behavior is removed.

---

-i needed no work and has been closed out

This issue used to cover -i as well. It does not any more, because the
behavior as65 documents was already unconditional here.

-i — "Ignore case in opcodes. In this way, the assembler does not
differentiate between adc and ADC, for example. Labels are still case
sensitive."

Measured with no flags given at all: lda #$42, LDA #$42 and Lda #$42
assemble to identical bytes, and a label defined Foo and referenced FOO is
an undefined symbol with or without -i. That is exactly the asymmetry as65
specifies, so -i is a no-op because the requested behavior is already the
default — not because it is missing.

Done on 020-disk-file-access:

• The help said "not implemented" and now reads
  Case-insensitive opcodes. Already the default; accepted as a no-op.
• ignoreOpcodeCase is deleted. Nothing read it and nothing could; a stored
  true in two structs invited somebody to build a conditional case-folding the
  assembler does not need. -i is still accepted and still concatenates.
• AssemblerTests pins the opcode behavior against the assembler, so the help
  and the code cannot drift apart on it.

Also closed out since this was filed

• caseSensitive rename. The field was renamed to ignoreOpcodeCase and has
  now been removed entirely.
• --cpu removed in favor of as65's -x. Done on 020-disk-file-access.
  This has a known cost on spec 019, which pins --cpu in as65 mode with its
  own tests and refuses --cpu by name on its Merlin path; whoever merges the two
  branches owns retargeting those at -x.
• Exit code 4. Now documented in the assembler's exit-code list as as65's
  out-of-memory status, which this tool never returns.