C API: Rework and enhance the PyBytesWriter implementation #158585

Placeholder issue to keep track of changes to rework and enhance the PyBytesWriter implementation.

Linked PRs

• gh-158585: Optimize PyBytesWriter_FinishWithSize() #158586
• gh-158585: Fix _PyBytes_Resize() if hash value is already computed #158589
• gh-158585: Use PyBytesWriter in io.BufferedReader.readline() #158615
• gh-158585: Don't overallocate at first PyBytesWriter_Resize() #158616
• gh-158585: Adjust allocation in bytes_fromformat() #158621