`fmpq_inv` may return 1/0, `fmpq_set_str` returns in non-canonical form

[mozhewen]

Describe the bug
fmpq_inv of zero returns 1/0.
fmpq_set_str only converts the str literally. For example, "4/6" -> 4/6.

Steps to reproduce

Expected behavior
fmpq_inv may throw a "Division by zero" exception, consistent with fmpq_div.
Not sure if the behavior of fmpq_set_str is intended.

System (please complete the following information):

• System CPU: MacBook Pro Apple M1 Pro
• Version of FLINT (if using Git, please specify commit): 3.3.1
• How FLINT was configured (i.e. options pushed): Installed from homebrew
• Output of configure Default configurations

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Additional context
Add any other context about the problem here.