fix: setting value persistence on SQL Server

[michalsn]

Description
This PR fixes SQLSRV persistence errors caused by storing setting values in the deprecated TEXT column type. For SQLSRV databases, the value column is migrated to VARCHAR(MAX) while other database drivers remain unchanged.

Boolean values are now serialized as '1' and '0', preventing mixed-type batch insert failures. Existing stored settings are preserved, and the migration is compatible with SQL Server 2022 and 2025.

Ref:

• https://learn.microsoft.com/en-us/sql/t-sql/data-types/ntext-text-and-image-transact-sql?view=sql-server-ver17
• Initial tests run with 2025 version: https://github.com/michalsn/settings/actions/runs/29758096213/job/88405573815
• Test without "serialize boolean" changes: https://github.com/michalsn/settings/actions/runs/29759235767/job/88409396104

Fixes #171

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide