fuzz: increase txorphan harness stability

Summary:
Backport of core#30186 and core#30306.

Note that we don't have the fuzz test yet, the point is to get the module up-to-date with upstream.

Depends on D16505.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16507