fix(payments): accept strict models, reused instances and string ids

[jfrosorio]

Description

Fixes the problems the package review found in the payment classes and traits. Every change is backward compatible.

• References now store only the model's fillable attributes. The API result also carries keys that are not columns (success, response, and status for Credit Card), which a model with Model::shouldBeStrict() or preventSilentlyDiscardingAttributes() refused after Eupago had already created the payment.
• create(), status() and refund() (and Credit Card's create()) start with an empty error bag, so hasErrors() on a reused instance reports only the latest operation instead of earlier failures.
• MBWay and createMbwayReference() take int|string $id, so string order ids work and zero-padded ids reach Eupago unchanged. Integer callers, including under strict_types, keep working.
• MB and createMbReference() take DateTimeInterface dates, so CarbonImmutable is accepted.
• refund() URL-encodes the transaction id in the request path.

Each fix has a test that fails without it.

Fixes

This fixes #96.

[Copilot]

Copilot review overview

🟢 Approval recommended

The changes align with the documented issue, are narrowly scoped, and are covered by targeted regression tests for the reported failure modes.

Review effort: Lite
Findings: None

What changed in this PR

This PR addresses several correctness issues in the EuPago payment helpers that were surfaced in issue #96, focusing on compatibility with strict Eloquent models, safe reuse of payment instances, and accepting broader input types for identifiers and dates.

Changes:

• Persist only model-fillable reference attributes (avoids strict-model failures when API responses include non-column keys).
• Reset the internal error bag at the start of create(), status(), and refund() (and Credit Card create()) so reused instances report only the latest operation’s errors.
• Broaden accepted types: MBWay identifiers now accept int|string, MB reference dates now accept DateTimeInterface, and refund() URL-encodes the transaction id in the request path.

File	Description
tests/​Feature/​TraitHelpersTest.php	Adds regression tests for strict models, immutable dates, and string MB Way ids.
tests/​Feature/​RefundTest.php	Adds tests for URL-encoding refund transaction ids and clearing errors on reused instances.
src/​Traits/​HasMultibancoReferences.php	Accepts DateTimeInterface for MB reference dates to support immutable dates.
src/​Traits/​HasMbWayReferences.php	Accepts `int
src/​Traits/​CreatesEuPagoReferences.php	Persists only fillable attributes when creating related reference models.
src/​MBWay/​MBWay.php	Updates MB Way identifier typing to `int
src/​MB/​MB.php	Accepts DateTimeInterface and formats dates for requests.
src/​EuPago.php	Clears errors at operation start and URL-encodes refund transaction id in the request path.
src/​CreditCard/​CreditCard.php	Clears errors at Credit Card create() start for reused instances.
docs/​mbway.md	Updates docs to reflect identifier is no longer limited to int.

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