* [Postgres] Add column statistics collection

Add a new column stats collector that queries pg_stats via the
datadog.column_stats() function and submits column-level statistics
(avg_width, n_distinct, null_frac) to the dbm-column-stats pipeline.

Key features:
- Streams results via cursor with configurable statement_timeout
- Chunks payloads at 5,000 columns to limit memory footprint
- Flushes at database boundaries to prevent cross-database accumulation
- Multi-database support via autodiscovery with per-database error isolation
- Health events for missing function and insufficient privileges
- Recovery detection when errors resolve
- Table include/exclude filtering pushed into SQL
- APM tracing via @tracked_method

* [Postgres] Move database_monitoring_column_stats to PostgreSql

Column statistics is currently a postgres-only feature, so the EvP
submission helper does not belong on the shared DatabaseCheck base.
Define it on the PostgreSql class instead. If MySQL or SQL Server
later add column-stats collectors, the method can be promoted up to
db.py without caller-side changes.

This also avoids cross-package release sequencing: a postgres PR
importing a new datadog_checks_base API would have to wait on a base
release before merging.

* [Postgres] Add regression tests for schema collector include filters

Existing schemas tests covered the exclude_databases / exclude_schemas /
exclude_tables paths but never include_*. Add coverage for the include
paths and for include + exclude combinations across all three filter
levels.

These tests serve as a baseline before refactoring the filter-clause
construction into a shared helper used by both the schemas and
column_stats collectors.

* [Postgres] Share filter clause helpers between schemas and column_stats

Extract two small helpers — regex_exclude_clauses and regex_include_clause
— into a new filters module, and use them from both the schemas and
column_stats collectors. The schemas methods (_get_schemas_query,
_get_tables_query) keep the same shape and behavior; column_stats's
_build_filters now composes both schema and table filters via the same
helpers.

While we are here, bring column_stats's filter set up to parity with
schemas by adding include_databases / exclude_databases (applied in
Python against the autodiscovered list) and include_schemas /
exclude_schemas (applied in SQL via the shared helpers). All four are
empty by default.

Coverage:
- Unit tests for the helpers in test_filters.py (12 cases).
- Integration tests in test_column_stats.py for include_schemas,
  exclude_schemas, include_and_exclude_schemas, include_databases,
  exclude_databases, include_and_exclude_databases.
- test_config_defaults updated for the four new knobs.

* [Postgres] Default collect_column_stats.enabled to false

Customers must opt in by setting collect_column_stats.enabled: true in
their instance config. Matches the default-off posture used by
collect_schemas.

* [Postgres] Update test_config feature checks for default-off column stats

test_initialize_features_enabled_and_disabled relied on collect_column_stats
defaulting to true; now that it defaults to false, enable it explicitly
alongside the other features. Also assert it is disabled in the
disabled-by-default test.

* [Postgres] Parameterize regex include/exclude filters

Address review feedback to switch from f-string interpolation to psycopg
parameterized queries for the regex-based include/exclude filters.

Helpers in filters.py now produce only `%s` placeholders, and the
collectors thread the pattern values through cursor.execute(query, params).
Mirrors the pattern already used by schemas._get_databases().

Changes:
- filters.py: helpers emit `%s` placeholders; pattern values no longer
  appear in the SQL string.
- column_stats._build_filters returns (sql, params); _collect_for_database
  passes params to cursor.execute.
- schemas._get_schemas_query / _get_tables_query / get_rows_query now
  return (sql, params); _get_cursor unpacks; _get_databases refactored
  to use the helpers.
- SCHEMA_QUERY: escape literal % as %% in LIKE clauses now that the
  query goes through parameterized execute.
- test_filters: assertions now check placeholder shape, not pattern values.
- test_column_stats: split special-chars test into two clearer tests
  (one for valid patterns containing quotes, one for invalid regex).

* [Postgres] Rename column_stats to column_statistics throughout

Use the full word 'column_statistics' instead of the abbreviated
'column_stats' for the new collector. Renames symbols, config keys, file
names, metric names, the SECURITY DEFINER function, the EvP track type,
and the dbm_type payload field.

Companion agent forwarder PR and backend dbm-metrics-intake registration
will be updated to match in a follow-up.

* [Postgres] Column statistics: tighten defaults, GCD scheduling, add diagnose probe

* [Postgres] Release column statistics collector on cancel

* [Postgres] Collect inherited, correlation, most_common_freqs in column statistics

* [Postgres] Capture column statistics collector before cancel in default-config test

* [Postgres] Address column statistics review feedback

* [Postgres] Drop column_statistics.max_query_duration config