perf: Inline an addToList, and reserved space for the list

Replaces a generic `addToList` helper call per element with an inlined `list.add(...)`, and pre-sizes the list via `ensureCapacity`.

**Benefit:** avoids repeated list growth/copy for large packed lists.

PR: hashgraph/pbj#914

Start by reviewing PR hashgraph/pbj#914, which contains the work described in this issue. Confirm the relevant generated-list paths and existing performance tests there, then verify that addToList calls are inlined and list capacity is reserved without changing behavior or breaking the test suite.

Written by the indexing model from the issue text.