Retire the byte-for-byte fidelity constraint, and fix what it was blocking

The Go reference is deprecated and will not be updated, so the two projects
are no longer required to match. Recorded as TODO.md section 0.1, first thing
in the file, because it silently reverses the premise several later sections
were written on -- an agent reading section 6 without it will park work that
is no longer blocked.

Section 6 item 16 was the item waiting on exactly this and is now fixed: the
keyword tables are searched on the base name with any type suffix stripped, so
PRINT$, LEN# and GOTO% are refused as variable names and the reference's own
diagnostic stops being dead code. It cost the one golden case predicted, and
the cost was nothing -- renaming a variable in strreverse.bas left its expected
output byte-for-byte unchanged.

AKBASIC_KNOWN_FAILING_TESTS is empty as a result and known_reference_defects.c
is gone. Section 6 items 1-9 and 11 are reopened as an ordinary defect list.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/reference/examples/strreverse.bas

@@ -1,7 +1,7 @@
-10 INPUT$ = "HELLO"
-20 STRLEN# = LEN(INPUT$) - 1
+10 SOURCE$ = "HELLO"
+20 STRLEN# = LEN(SOURCE$) - 1
 30 REV$ = ""
 40 FOR I# = STRLEN# TO 0 STEP -1
-50   REV$ = REV$ + MID(INPUT$, I#, 1)
+50   REV$ = REV$ + MID(SOURCE$, I#, 1)
 60 NEXT I#
 70 PRINT "REVERSED: " + REV$