fix(entry-query): remove get_all_entries_asc

[faisalahammad]

Summary

get_all_entries_asc() cached a Liveblog post's entire entry list under one cache key. On posts with a lot of entries that blob can exceed the memcache 1MB object size limit, so the write silently fails and every request falls back to a full uncached DB read - exactly the scaling problem this was meant to avoid. This replaces it with direct, date-bounded DB queries and a small cached count for pagination.

Fixes #591

Changes

classes/class-wpcom-liveblog-entry-query.php

Before:

public function get_between_timestamps( $start_timestamp, $end_timestamp ) {
	$all_entries = $this->get_all_entries_asc();
	return $this->find_between_timestamps( $all_entries, $start_timestamp, $end_timestamp );
}

public function get_all_entries_asc() {
	$cached_entries_asc_key = $this->key . '_entries_asc_' . $this->post_id;
	$cached_entries_asc     = wp_cache_get( $cached_entries_asc_key, 'liveblog' );
	if ( false !== $cached_entries_asc ) {
		return $cached_entries_asc;
	}
	$all_entries_asc = $this->get( array( 'order' => 'ASC' ) );
	wp_cache_set( $cached_entries_asc_key, $all_entries_asc, 'liveblog' );
	return $all_entries_asc;
}

After:

public function get_between_timestamps( $start_timestamp, $end_timestamp ) {
	$args = array(
		'order'      => 'ASC',
		'date_query' => array(
			'column'    => 'comment_date_gmt',
			'after'     => gmdate( 'Y-m-d H:i:s', $start_timestamp ),
			'before'    => gmdate( 'Y-m-d H:i:s', $end_timestamp ),
			'inclusive' => true,
		),
	);
	$entries = $this->get( $args );
	return self::remove_replaced_entries( $entries );
}

public function count_entries() {
	// keys a small cached count off the highest comment ID (not timestamp,
	// so same-second inserts can't collide), excludes deletions and
	// original entries that have since been replaced by an edit or delete
	...
}

Why: queries the requested time range directly from the DB instead of loading and caching the whole entry list. count_entries() gives get_entries_by_time() a correctly deduplicated pagination count without needing the full list either.

liveblog.php

Before:

$all_entries = self::$entry_query->get_all_entries_asc();
$entries     = self::$entry_query->find_between_timestamps( $all_entries, $start_timestamp, $end_timestamp );
...
$pages = ceil( count( self::flatten_entries( $all_entries ) ) / $per_page );

After:

$entries = self::$entry_query->get_between_timestamps( $start_timestamp, $end_timestamp );
...
$pages = ceil( self::$entry_query->count_entries() / $per_page );

Why: get_entries_by_time() is hit on every polling request, so it's the method that actually blows past the cache size limit on large liveblogs. get_entries_paged() was changed similarly, just querying the full ASC list directly instead of caching it as one object - its pagination math is unchanged.

Testing

Test 1: date-bounded query returns the right entries

1. Added entries in tests/Integration/EntryQueryTest.php covering get_between_timestamps() against the new date_query path (mid-range, border timestamps)
   Result: passes, same coverage as before plus new count_entries() tests for inserts, deletions, and edits.

Test 2: pagination unaffected

1. Added tests/Integration/RestApiTest.php coverage for get_entries_paged() - page slicing, empty state, deleted entries excluded from total
   Result: passes

Test 3: full suite

1. composer test:unit - 7 tests, composer test:integration - 166 tests, composer cs on changed files, composer lint
   Result: all pass, 0 PHPCS errors/warnings on changed files

Screenshots

N/A, no UI changes.