[Repo Assist] feat: add fold, foldBack, find, tryFind, pick, tryPick, filter, choose, partition, scan, indexed, unzip, pairwise, groupBy, max, min to NonEmptyList

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Closes #174

Summary

Adds 16 missing standard List-equivalent functions to the NonEmptyList module, addressing the long-standing gap identified in #174.

Functions Added

Function	Return Type	Notes
fold	'State	Left fold, like List.fold
foldBack	'State	Right fold, like List.foldBack
find	'T	Raises KeyNotFoundException if not found
tryFind	'T option	Returns Some x for the first element where predicate returns true; None if none match
pick	'U	Raises KeyNotFoundException if chooser never returns Some
tryPick	'U option	Returns the first Some result from chooser, or None
filter	'T list	Returns plain list (result can be empty)
choose	'U list	Filter + map; returns plain list
partition	'T list * 'T list	Both halves may be empty
indexed	NonEmptyList<int * 'T>	Pairs each element with its index
unzip	NonEmptyList<'T1> * NonEmptyList<'T2>	Splits a list of pairs
pairwise	('T * 'T) list	Adjacent pairs; empty for singleton
scan	NonEmptyList<'State>	Always non-empty (includes initial state)
groupBy	NonEmptyList<'Key * NonEmptyList<'T>>	Non-empty; each group is non-empty
max	'T	Safe since list is always non-empty
min	'T	Safe since list is always non-empty

Design principle: functions that cannot produce an empty result return NonEmptyList<_>; functions that can produce an empty result return a plain 'T list.

Tests

18 property-based tests added to NonEmptyListTests.fs, verifying consistency with List module equivalents.

Test Status

✅ All tests pass on ubuntu-latest via dotnet test. Fantomas formatting check passes.

[Copilot]

Pull request overview

This PR fills a long-standing API gap by adding missing List-equivalent operations to NonEmptyList, while preserving the design rule that only operations guaranteed to stay non-empty return NonEmptyList<_>.

Changes:

• Added 14 List-equivalent functions to src/FSharpx.Collections/NonEmptyList.fs (e.g., fold, find, filter, scan, groupBy, max/min).
• Added property-based tests to validate behavior matches List equivalents in tests/FSharpx.Collections.Tests/NonEmptyListTests.fs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/FSharpx.Collections/NonEmptyList.fs	Adds missing List-equivalent functions to NonEmptyList with appropriate return types (non-empty vs possibly empty).
tests/FSharpx.Collections.Tests/NonEmptyListTests.fs	Adds property-based tests comparing new NonEmptyList functions against List behavior.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.