DAOS-19210 dfs: show progressive-layout info in daos cont query and f…

[mchaarawi]

…s get-attr

The daos tool previously reported only a single file object class and did not show PL details, so daos cont query and daos fs get-attr gave an incomplete picture of PL files/containers.

Generalize the DFS query/info API to a head plus an ordered array of tail segments so it also covers a future head + N tails:

• Add dfs_pl_seg_t {oclass, split_off, oid} and DFS_PL_MAX_SEGMENTS.
• dfs_attr_t: da_file_oclass_id is the head class in the PL case; add da_file_pl_nr + da_file_pl_segs[] for the tail segment(s). Populated by dfs_query().
• dfs_obj_info_t: add doi_pl_nr + doi_pl_segs[]; drop the single-tail fields. Populated by dfs_obj_get_info() for files (real tail oids) and for directories (file-creation template, nil oids).
• Refactor file_oclasses() to take a parent oclass and add dfs_default_file_pl() so the container/dir default layout can be resolved without an open file object.

daos tool:

• cont query: print File Head/Tail Object Class and Split Offset per tail segment when PL applies (File Object Class alone otherwise).
• fs get-attr on a file: print Head/Tail OID, Head/Tail Object Class, and Split Offset; on a directory: print the file-creation head/tail classes and split offset. JSON output extended with a tails/pl array.
• Plumb the new fields through POSIXAttributes and the libdfs/libdaos bindings and stubs.

Update the DFS unit test to the new doi_pl_nr/doi_pl_segs fields.

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 'update daos tool to return PL oclasses and not just the head'
Status is 'In Progress'
https://daosio.atlassian.net/browse/DAOS-19210

[daosbuild3]

Test stage Functional Hardware Large MD on SSD completed with status UNSTABLE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net/job/daos-stack/job/daos//view/change-requests/job/PR-18632/4/testReport/

[daosbuild3]

Test stage Functional on EL 9 completed with status FAILURE. https://jenkins-3.daos.hpc.amslabs.hpecorp.net//job/daos-stack/job/daos/view/change-requests/job/PR-18632/5/execution/node/1369/log