feat: OverwriteAction support (replace all / partial overwrite)

[gbrgr]

Summary

Adds atomic overwrite snapshot support to RustyIceberg.jl, enabling callers to replace all (or a subset of) existing Parquet files with a new set in a single Iceberg Operation::Overwrite snapshot.

Depends on: RelationalAI/iceberg-rust#76 (cherry-pick of upstream apache/iceberg-rust#2185, which adds OverwriteAction to iceberg-rust).

Changes

FFI (iceberg_rust_ffi/src/transaction.rs)

• IcebergOverwriteAction — accumulates added + deleted DataFile lists
• iceberg_overwrite_action_new / _free
• iceberg_overwrite_action_add_data_files — move new files into action
• iceberg_overwrite_action_delete_data_files — move files-to-delete into action
• iceberg_overwrite_action_apply — calls Transaction::overwrite().apply()
• iceberg_table_list_data_files — async walk of manifest list to collect all live DataFile records from the current snapshot

Julia bindings (src/transaction.jl)

• OverwriteAction struct + constructor / free_overwrite_action!
• add_data_files(action, files) / delete_data_files(action, files)
• apply(action, tx) / with_overwrite(f, tx) convenience helper
• list_data_files(table) -> DataFiles
• All new symbols exported from RustyIceberg

Tests (test/overwrite_tests.jl)

Self-contained, no Docker — all tests use mktempdir + catalog_create_memory:

• OverwriteAction lifecycle (new / free / double-free)
• list_data_files on empty table
• list_data_files after append
• Overwrite replaces all existing files
• Overwrite deletes only explicitly listed files; others survive intact
• Overwrite add-only (no deletes) produces a new snapshot
• Two sequential overwrites converge correctly
• Error handling: freed action, null DataFiles, committed (consumed) transaction

Usage

# Replace all existing files atomically
old_files = list_data_files(table)
new_files = RustyIceberg.with_data_file_writer(table) do w
    write(w, new_data)
end
updated_table = with_transaction(table, catalog) do tx
    with_overwrite(tx) do action
        add_data_files(action, new_files)
        delete_data_files(action, old_files)
    end
end

Test plan

• make run-containers && make test passes (all overwrite testsets green)
• Existing test suite unaffected (27875 pre-existing tests still pass)

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