Fetch snapshot specific partition spec

The spec id expected in `getTable` is expected to be spec as_of snapshot. Currently the one used is spec of an iceberg table, `iceTable.spec()` should return current spec id. This spec may not be valid for the given snapshot.

_Originally posted by @ashvina in https://github.com/onetable-io/onetable/pull/111#discussion_r1373780190_

Start by tracing getTable and how it obtains the partition spec from iceTable.spec(). Compare that current table spec with the spec associated with the requested snapshot; done means getTable uses the snapshot-specific spec and remains valid for that snapshot.

Written by the indexing model from the issue text.