Fix type safety and formatting issues in provider code

[Copilot]

This PR addresses three type safety and formatting issues identified in the codebase to improve code reliability and user experience.

Changes Made

Issue 1: Missing String Validation in Billing Policy Resource

Added stringvalidator.LengthAtLeast(1) validation to required string attributes in resource_billing_policy.go:

• name attribute
• location attribute
• billing_instrument.resource_group attribute
• billing_instrument.subscription_id attribute

This prevents empty strings from being passed to the API, which could cause confusing errors for users.

Issue 2: Interface Implementation Assertion in UrlFormatError

Updated UrlFormatError in internal/customerrors/url_format_error.go to use pointer receivers for better maintainability:

• Changed interface assertion from var _ error = UrlFormatError{} to var _ error = (*UrlFormatError)(nil)
• Updated Error() and Unwrap() methods to use pointer receivers (*UrlFormatError)
• Fixed related test case in client_test.go to check for pointer type

This follows Go best practices and ensures future-proofing if the error type needs to be extended.

Issue 3: Escaped Newlines in UUID Error Messages

Fixed newline formatting in internal/customtypes/uuid_value.go:

• Changed UUIDTypeErrorInvalidStringDetails from raw string literal with literal \n to regular string literal with proper escape sequences
• Error messages now display proper line breaks instead of literal \n characters

Before:

A string value was provided that is not valid UUID string format.\n\nGiven Value: invalid-uuid\n

After:

A string value was provided that is not valid UUID string format.

Given Value: invalid-uuid

Testing

• All changes pass linting with make lint
• Code builds successfully with make build
• Documentation generation completes without errors with make userdocs
• No regressions introduced in existing functionality

Fixes #825.

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[Copilot]

Pull Request Overview

This PR improves type safety and formatting in provider-related code to enhance reliability and user experience.

• Added string validation for required attributes in the billing policy resource.
• Updated error type assertions and pointer receiver usage for URL format errors.
• Corrected newline formatting in UUID error messages and updated corresponding tests.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/services/licensing/resource_billing_policy.go	Added string validators for required fields to prevent empty inputs.
internal/customtypes/uuid_value.go	Changed UUID error message literal to enable proper newline formatting.
internal/customerrors/url_format_error.go	Updated error type assertion and methods to use pointer receivers.
internal/api/client_test.go	Modified test case for error type to align with pointer receiver implementation.
.changes/unreleased/fixed_type_safety_formatting_issues.yaml	Documented the fixed type safety and formatting issues.