Add getBool() and getInt() to Config and use them instead of filter_var and (int) in the framework #616

Summary

Add getBool() and getInt() to Config and use them in the framework instead of the scattered filter_var(..., FILTER_VALIDATE_BOOLEAN) and (int) conversions. Depends on #615.

Why

The framework converts config values by itself in about ten places, because a config file stores whatever env() returned, and env() returns text. This cannot simply be dropped: 'debug' => env('DEBUG', true) stores the string 'true' or 'false' whenever .env has a DEBUG line, which is how every project created from the starter project works. So the conversion stays at the read, in one place, until a major version can require real types.

Where it happens today

• filter_var(..., FILTER_VALIDATE_BOOLEAN): is_debug_mode() and Debugger (app.debug), MailerTrait (mailer.mail_trap), ViewCache (resource_cache, view_cache.minify), AuthTrait (two_fa), Lang RemoteAdapterTrait (cache.enabled, use_source_catalog), and the two_fa check in the DemoApi and DemoWeb AuthController templates.
• (int) on a config value: logging.message.limit, mailer.transport_log_limit, view_cache.ttl, lang.url_segment, the cache adapters' port, and the remember-me lifetime.
• No conversion at all: the SMTP port, the ttl of the cache and rate limiter adapters, and the enabled flag in ModuleLoader ((bool) "false" is true).

Proposed change

• ConfigInterface and Config get getBool(string $key, bool $default = false): bool and getInt(string $key, int $default = 0): int, with the same rules as the Environment readers (Add getBool() and getInt() to Environment, with env_bool() and env_int() helpers #615). The rules should live in one place, not be copied.
• Replace the reads above with them. Some of those values come from an adapter's params array and not from a config key; decide for each whether to read the key through Config or to keep a local conversion.
• Behavior stays the same for booleans. For integers, text that is not a whole number now throws instead of becoming 0; call that out in the changelog.

Out of scope

• Trusting the config types and removing the safety net. That breaks every project whose config still says env('DEBUG', true), so it belongs to 4.0.0.

Breaking changes

• None for valid values. An invalid integer in config now throws instead of becoming 0.

Acceptance criteria

• no filter_var(..., FILTER_VALIDATE_BOOLEAN) and no (int) of a config value is left in src, or each one that stays has a reason
• tests cover both methods, and the places changed keep their existing tests green
• composer test, composer cs:check, composer phpstan and composer rector:check pass on every PHP version in the CI matrix
• the changelog lists the change