fix: report worker activity to pg_stat_activity

[utkarash2991]

Problem

The pg_net background worker doesn't call pgstat_report_activity(), so its row in pg_stat_activity shows up with blank state, query, query_start, xact_start, and state_change columns. This makes it impossible to tell from monitoring whether the worker is idle, processing a tick, or stuck in a transaction.

Regular user backends get this for free via tcop/postgres.c. Background workers must do it themselves.

Fix

Add pgstat_report_activity transitions around the inner work loop:

• STATE_IDLE initially (worker starts by waiting for a wake)
• STATE_RUNNING when the worker enters the inner work loop
• STATE_IDLE when the inner loop drains and the worker goes back to waiting

cmd_str = NULL, matching what other background workers do (logical replication apply worker, walsender on idle). backend_type already identifies the row as "pg_net <ver> worker", so a query-column label would be redundant.

Verification

Sample output before/after on a local repro:

Before (backend_type ilike '%pg_net%'):

 pid | backend_type         | state | wait_event
-----+----------------------+-------+-----------
 218 | pg_net 0.20.2 worker |       | Extension

After, at rest:

 pid | backend_type         | state | wait_event
-----+----------------------+-------+-----------
 218 | pg_net 0.20.2 worker | idle  | Extension

After, while processing a tick:

 pid | backend_type         | state  | wait_event
-----+----------------------+--------+-----------
 218 | pg_net 0.20.2 worker | active | Extension

Refs PSQL-1221, follow-up to #254.

[steve-chavez]

@utkarash2991 Can we test this somehow?

[utkarash2991]

@utkarash2991 Can we test this somehow?

@steve-chavez Added a regression test in 8ec2990. It asserts pg_stat_activity.state shows 'idle' at rest and 'active' during a slow request (using delay=2 so the active window is observable). Please let me know how this looks .

[utkarash2991]

@utkarash2991 Can we test this somehow?

@steve-chavez Added a regression test in 8ec2990. It asserts pg_stat_activity.state shows 'idle' at rest and 'active' during a slow request (using delay=2 so the active window is observable). Please let me know how this looks .

@steve-chavez does the changes looks good to you ? ok to merge ?

[steve-chavez]

LGTM 👍