fix(process manager): apply limit and offset in get_jobs

[C1-BA-B1-F3]

Summary

The PostgreSQL and MongoDB process managers ignored the limit and offset parameters in get_jobs, returning all jobs regardless of the query string. The TinyDB manager already applied both correctly.

This PR adds offset then limit to both backends, matching the TinyDB behaviour.

Changes

• pygeoapi/process/manager/postgresql.py: add .offset() / .limit() to the SQLAlchemy query
• pygeoapi/process/manager/mongodb_.py: add .skip() / .limit() to the PyMongo cursor

Test plan

• pytest tests/manager/test_manager.py — 4/4 pass
• pytest tests/manager/test_tinydb_manager_for_parallel_requests.py — 1/1 pass
• PostgreSQL integration tests require a live database and were not run locally; the change is confined to the query builder and mirrors the existing TinyDB pattern.

Fixes #2426

[C1-BA-B1-F3]

Correcting the CI evidence in my earlier comment: the Build failure has a single root cause, it is not caused by this PR, and my earlier pointer to the 2026-09-29 templating run was wrong (that run failed only on test_postgresql_provider with ModuleNotFoundError: No module named 'psycopg', not on these two tests).

Root cause

The usgs-prism collection fails to load:

WARNING pygeoapi.provider.xarray_:xarray_.py:114
        open_group() got an unexpected keyword argument 'zarr_format'
WARNING pygeoapi.api:__init__.py:956
        Error generating collection usgs-prism: open_group() got an unexpected
        keyword argument 'zarr_format'

That single failure produces both red tests: describe_collections sees 9 collections instead of 10, and every EDR query against usgs-prism returns 500 (ProviderNoDataError -> test_get_collection_edr_query).

Why it is environmental, not this PR

• The last green Build runs — master (2026-09-22) and the psycopg branch (2026-09-29) — installed xarray 2026.7.0.
• The runs from 2026-10-03 install xarray 2026.9.0. zarr is unchanged at 2.18.7 (pinned <3).
• requirements-provider.txt leaves xarray unpinned, and 2026.9.0 changes the Zarr open path, which breaks pygeoapi/provider/xarray_.py for the usgs-prism Zarr store.

This PR only touches pygeoapi/process/manager/postgresql.py` and `pygeoapi/process/manager/mongodb_.py; it does not touch the EDR/xarray provider or the collection config. Happy to rebase once the environment (or the xarray pin) is fixed.