[Update] make `CellValue` internal

[john-dc252]

Changes:

• change visibility of CellValue to pub(crate)
• remove internally unused methods that return CellValue

[john-dc252]

Since mutators and accessors are already available through Cell, would it not be better to exclude the CellValue type from the public API?

[MathNya]

john-dc252

Since mutators and accessors are already available through Cell, would it not be better to exclude the CellValue type from the public API?

Sorry for the late reply. The CellValue API, I think it would be useful to have. Like when preparing a CellValue and applying it to multiple Cells. If this is the case, I feel that Cell's set_value_from_string etc. is unnecessary. As for the system, I want to keep it as simple as possible. Hmmm, I will consider this a little.