Throw TypeError when container factory returns Closure

[clue]

This changeset adds improved type checking for container factory functions to ensure they return the expected value instead of a Closure. Factory functions in the container configuration remain fully supported and continue to work as before, but their return value must be a usable value (object, scalar, or null) rather than another function:

$container = new Container([
    'X_VALID' => function () { // supported: factory returns a string value
        return 'bar';
    },
    'X_INVALID' => function () { // error: factory returns a Closure instead of the expected value
        return function () {
            return 'bar';
        };
    },
    'X_FOO' => function ($X_VALID, $X_INVALID) {
    
    };
]);

This includes a number of updated tests to verify correct behavior and avoid introducing any potential regressions, so this has 100% code coverage and should be safe to apply. For class-type factories, this case is already caught by the existing type checks. For variable factories, a Closure is technically an object and would previously pass the type checks silently but would trigger a different return value on the next invocation. This adds an explicit check to catch this early.

Builds on top of #301, #284 and others

[Copilot]

Pull request overview

This PR tightens type validation for container variable factory functions by explicitly rejecting factories that return a Closure, preventing accidental “factory returning a factory” behavior and surfacing a clear TypeError earlier.

Changes:

• Add an explicit Closure return-value check for variable factories in Container::loadVariable() and throw TypeError.
• Add PHPUnit coverage for the new behavior when calling getEnv() and to assert class-factory behavior remains consistent for getObject().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Container.php	Adds explicit rejection of Closure return values from variable factories via a dedicated TypeError.
tests/ContainerTest.php	Adds tests ensuring getEnv() rejects factories returning a Closure and getObject() continues to error consistently when a class factory returns a Closure.

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