unmodifiableList instead of List.copyOf in Try

Context

Try.Partition and the Try collectors return immutable lists of successful values. Try.run() produces Success(null), and those nulls can appear in the result lists of sequence/partitioningBy.

Decision

Try uses Collections.unmodifiableList(new ArrayList<>(...)) instead of List.copyOf for lists of successful values.

Consequences

Positive:

• Preserves null elements in the list (produced by Try.run()).
• sequence(List.of(Try.run(() -> {}))) returns Success([null]) without throwing NPE.

Negative / tradeoffs:

• unmodifiableList allows null internally; List.copyOf is stricter and clearer about nullability.
• Behavioural difference with Result, which does use List.copyOf (because Ok guarantees non-null).

Alternatives considered

• List.copyOf in both: breaks compatibility with Try.run() and Try<Void>.
• Prohibit null in Success: removes the ability to represent void side-effects without a Unit type.