linter: split require-timeout-settings into require-lock-timeout and require-statement-timeout

[zvdy]

Fixes sbdchd#1231

What

Splits the require-timeout-settings rule into two independent rules so each timeout check can be enabled/disabled on its own:

• require-lock-timeout — warns when set lock_timeout is missing before potentially slow operations
• require-statement-timeout — warns when set statement_timeout is missing before potentially slow operations

Both are enabled by default (same effective default behavior as before, only the violation codes change).

Backwards compatibility

require-timeout-settings is kept as a deprecated alias that expands to both granular rules:

• excluded_rules = ["require-timeout-settings"] still disables both checks
• included_rules = ["require-timeout-settings"] enables both
• -- squawk-ignore require-timeout-settings comments still suppress both violations
• exclude wins over include: excluding require-statement-timeout while including the alias leaves only the lock check enabled

Example

$ squawk --exclude=require-statement-timeout mig.sql
mig.sql:0:0: warning: require-lock-timeout Missing `set lock_timeout` before potentially slow ACCESS EXCLUSIVE lock operations

Changes

• squawk_linter: new Rule::RequireLockTimeout / Rule::RequireStatementTimeout variants; the shared check in require_timeout_settings.rs now gates each report on its own rule and reports under the granular codes; alias expansion in Linter::from, Linter::with_rules, and squawk-ignore parsing
• tests for granular enable/disable, alias expansion in config and ignore comments; regenerated affected snapshots
• docs: new require-lock-timeout / require-statement-timeout pages, deprecation note on require-timeout-settings, sidebar + homepage rule list updates
• CHANGELOG entry