DAOS-18890 dfuse: Enhance error handling in close_dup_fd and finalize_myhook functions

[mchaarawi]

pil4dfs now disables interception at the start of the destructor path, before bulk fd/dirfd/DFS cleanup, so teardown does not re-enter interception logic while it is releasing tracked state.

duplicate-fd cleanup now validates the fake-fd slot before calling free_fd(), and fails cleanly with a log if the dup table points at an invalid or already-cleared fake fd instead of walking freed state and corrupting the heap.

Allow-unstable-test: true

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is 'dfuse/bash_fd.py:DFuseFdTest.test_bashfd_pil4dfs - ./bash_fd_outer.sh: line 11: 244212 Aborted'
Status is 'Open'
Labels: 'ci_master_weekly,intercept_lib,weekly_test'
Errors are Title of PR is too long
https://daosio.atlassian.net/browse/DAOS-18890