labs/lab-11: Add checker infrastructure

[teodutu]

Follow the structure in this task [1] to create tests for the following tasks:

entry-fix-1
entry-fix-2
export-fix
include-fix
lib-fix
multiple-link
obj-link-dev
single-link
var-func-fix
vars-obs

The students should just run make check in tasks/<task-name>/tests/ and receive the output of each test + the total number of points out of 100.

Steps to solve this:

1. Add the test harness files in the task-name/tests folder. The Makefile there should compile the code in ../support. The scripts below should get the output from running the compiled code and then compare it with some predefined values. Let's suppose a task has the following files:

   task-name/
   |-- support/
   |   |-- Makefile
   |   `-- main.c
   `-- solution/
       |-- Makefile
       `-- main.c
   

   This hierarchy should be changed as follows:

   task-name/
   |-- support/                # Unchanged
   |-- solution/               # Unchanged
   `-- tests/
       |-- Makefile            # Compiles the code in `support/` and runs run_all_test.sh
       |-- graded_test.inc.sh  # Boilerplate code for testing and printing. Required by every task
       |-- run_all_tets.sh     # Generic test runner
       `-- test.sh             # Contains tests for the tasks in ../support/main.c
   

2. Add a description to the task's README.md file about running the checker together with a full run that obtains 100 points, like so [2].

Refer to [1] for more information about the content of each file in tests/.
Read the contributor guidelines before making contributions [3].
Add Fixes #44 at the end of your commit message to automatically link your PR with this issue.

[1] https://github.com/cs-pub-ro/operating-systems/tree/main/chapters/data/memory-security/drills/tasks/stack-protector/solution/tests
[2] https://github.com/cs-pub-ro/operating-systems/blob/5db2ced28419f274cad0e0e6dab2ab2bb18de1f9/chapters/data/memory-security/drills/tasks/exec-shellcode/README.md?plain=1#L19-L40
[3] https://github.com/cs-pub-ro/hardware-software-interface/blob/main/CONTRIBUTING.md#pull-requests