feat(windows): allow forced PHP extensions

[rozsazoltan]

Summary

Adds an explicit Windows-only opt-in for extensions disabled by default because they require external native dependencies.

• Supports one-off PHP_WINDOWS_FORCE_EXTENSIONS values.
• Supports persistent _.php.windows_force_extensions configuration in mise.toml.
• Enables and verifies forced extensions during installation.
• Documents the Oracle Instant Client requirement for oci8_19 and pdo_oci.

Validation

• Lua syntax checks for the modified files.
• Environment parser and mise option bridge tests.
• Native Windows PHP 8.3.32 smoke test confirming the forced extensions are enabled and verified.
• Verified the expected installation failure when Oracle Instant Client is unavailable.