[r/python] Standardize mappings of native, Arrow, and TileDB types

[mojaveazure]

As described in #2698, the R and Python APIs don't always write out to the same TileDB type, leading to cases where a character in R could become a bytes in Python instead of a str; this issue is a tracking for various types in the high-level languages and their mappings in Arrow and libtiledbsoma

Examples showcasing string/character/bytes inputs: https://gist.github.com/mojaveazure/ce7b10447b85de1f360218b173f4516f

• Python str and R character

  • both should map to Arrow UTF8 and TILEDB_STRING_UTF8
  • R wrote group-level meta data as TILEDB_STRING_ASCII/TILEDB_CHAR, which mapped to Python bytes (resolved in [r] Write group-level string metadata as TILEDB_STRING_UTF8 #3469`)
  • array-level meta data in R does not have this issue
  • both types are disallowed as an array type
    • R allows writing character to sparse and dense arrays [r] Disallow writing character and raw arrays #3503
    • Python disallows this, but throws a cryptic error with dense arrays TypeError: Invalid pyarrow type string [python] Cryptic error messages when creating arrays of disallowed types #3504
    • pyarrow Tensors disallow str, so sparse arrays fail when trying to create a Tensor for writing
  • both types are allowed in data frames
    • both R and Python will write as Arrow UTF8, but read back as Large UTF8, irrespective of language used for writing or reading [r/python] Python str, R character, and Python bytes are cast to large variants #3507

• Python bytes and R raw

  • both should map to Arrow Binary and TILEDB_STRING_ASCII or TILEDB_CHAR (equivalent types)
  • Python writes bytes meta data as TILEDB_STRING_UTF8, resulting in these always being read back as str ([python] Group and array-level meta data written as bytes should be preserved as bytes #3502)
  • R does not support writing raw/arrow::binary() as meta data [r] Allow writing raw as metadata for groups and arrays #3505
  • both types are disallowed as an array type
    • R allows writing raw to sparse and dense arrays, but are cast to arrow::uint8() [r] Disallow writing character and raw arrays #3503
    • Python disallows this, but throws a cryptic error with dense arrays TypeError: Invalid pyarrow type string [python] Cryptic error messages when creating arrays of disallowed types #3504
    • pyarrow Tensors disallow bytes, so sparse arrays fail when trying to create a Tensor for writing
  • both types are allowed in data frames
    • Python writes as an Arrow Binary, but reads back in both Python and R as a Large Binary [r/python] Python str, R character, and Python bytes are cast to large variants #3507
    • Arrow-R maps raw to arrow::uint8(), this needs to be handled at the R level to map to arrow::binary() instead [r] Map raw to arrow::binary() #3506