Audit existing LAMBDAs for array-lifting support

[jimmytacks]

Summary

Per #179, audit every LAMBDA in the library for array-lifting support. Apply the dispatcher pattern wherever a scalar-input/scalar-output LAMBDA silently collapses or errors on array input.

Upgrades (⚠️ dispatcher added)

LAMBDA	Lift on	Reason
CELLTOPOS	cell	SUMPRODUCT(...SEQUENCE(LEN(letters))...) collapses arrays of addresses
POSTOCELL	pos	defensive; ADDRESS may lift naturally, dispatcher makes it explicit
MOVECELL	cell	calls CELLTOPOS internally
GRIDLOOKUP	value	forward (XMATCH) and reverse (CELLTOPOS) branches
INCEL	address	INDIRECT doesn't lift over arrays of addresses
NTH	n	@INDEX(flat, idx, 1) collapses to first when idx is array
CHARQ	Text	regex branch's COLUMNS(REGEXEXTRACT(...)) returns one array per Text, doesn't compose
REVERSESTRING	text	SEQUENCE(LEN(text), ...) errors when text is array
TLOOKUP	Item	defensive; MATCH may lift in modern Excel, dispatcher makes it explicit

Already lifts (✅ no change — confirmation tests added where relevant)

• CONTAINS — XMATCH lifts on value
• CIRCPOS — MOD lifts on moves and start (help already advertised this)
• GetVar / GetVarAt / SplitState — already MAP over a column of states

Skip (➖ no scalar input, or output inherently an array)

GRIDAREA, ARROWMOVES, DEFAULTARROWS, DEFAULTMOVEDELTAS, KNIGHTDELTAS, BICOL, BIROW, MAXOF, MINOF, NTHOCCURRENCE, CUMSUMGRID, MAXOCCUR, MINOCCUR, EXPANDDIMENSIONS, SNAQUENCE, WRITEAT, INSERTAT, REVERSEARRAY, ROTATE, EXPLODE, CONSECGROUPS, COMBINATIONS, COMBININDICES, SetVar, SetVars, SetState, NewState, FINDFIRST, FINDALL, REDUCEUNTIL, REDUCEWHILE, SCANUNTIL, SCANWHILE.

Dispatcher shape

The scalar body is preserved inline as a LAMBDA inside LET (rather than a separate <NAME>_SCALAR workbook name) — this keeps the namespace tidy and the logic in one file:

scalar, LAMBDA(c, LET(... scalar body ..., scalar result)),
result, IF(OR(ROWS(arg) > 1, COLUMNS(arg) > 1),
            MAP(arg, scalar),
            scalar(arg)),
IF(Help?, Help, result)

The dispatcher sits after the ISOMITTED(...) → ShowHelp branch, so =CELLTOPOS() etc. still return help text. Scalar callers are unaffected.

Test plan

• All existing scalar tests still pass (no regressions).
• 23 new tests added covering vertical, horizontal, and where useful 2D / range-of-cells inputs:
  • maps: CELLTOPOS (4), POSTOCELL (2), MOVECELL (2), GRIDLOOKUP (2), INCEL (2)
  • array: NTH (2), CONTAINS (1)
  • string: CHARQ (2), REVERSESTRING (2)
  • lookup: TLOOKUP (2)
  • math: CIRCPOS (2)
• dotnet test addin/lambda-boss.AddinTests — 382 pass (was 359 pre-change).
• dotnet test addin/lambda-boss.Tests — 828 pass.

Closes #179

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