feat: support BackedEnum values in database binds

[memleakd]

Description

This PR adds support for PHP BackedEnum values in database escaping, query bindings, and escaped Query Builder values.

It was inspired by @maniaba's forum post and #10223.

For apps that use native PHP enums for domain values, this makes database code a bit nicer to write:

$db->table('users')
    ->where('status', UserStatus::Active)
    ->get();

CodeIgniter will use the enum's backing value when escaping it, so string-backed enums are treated like strings and int-backed enums are treated like integers.

This avoids repeating ->value at every query call site, while keeping raw SQL and escape-disabled values in the caller's control.

The implementation is intentionally small: enum cases are unwrapped during database escaping, so regular query bindings and escaped Query Builder values use the same existing path.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[datamweb]

PR look good to me.

[michalsn]

Seems like native prepared statements are not supported.

$query = $db->prepare(...);
$query->execute(StatusEnum::ACTIVE);

[memleakd]

Seems like native prepared statements are not supported.

Thanks for the review. I pushed an update for adding prepared query support, object input coverage, and the SQL assertion helper.

[datamweb]

@memleakd Could you please implement the assertSqlEquals() and its usage in a separate Pull Request?
Also, please make sure to update the testing documentation accordingly here:
https://codeigniter4.github.io/userguide/testing/overview.html#id10

[memleakd]

@memleakd Could you please implement the assertSqlEquals() and its usage in a separate Pull Request?

That was my natural first instinct too, but I somehow got the impression from the review wording that it might be preferred here 😅 Anyway, I reverted it now, so this PR is clean again and only keeps the enum-related changes.