Contract with `threaded` method

[Delja]

This pr makes it possible to prevent that contracts in different threads to interfere with the same flag to know if a contract evaluation should be performed.

Instead of using a flag contained in the Sys instance, we are now using a new AST node which:

• During compilation it will be transformed into an if with for condition the evaluation of a variable whose value is specific to each threat (in_assertion). Note we used the keyword __thread.

• During the interpretation the node will be evaluated in the same way as an if (without anelse block) with for condition the value of the attribute in_assertion defined in the interpreter.

Note: When you evaluate a contract, the evaluation is performed in the same thread as the caller. (only the method will be executed in a new thread)

[github-actions[bot]]

Test Results

    67 files     338 suites   17m 34s :stopwatch: 14 192 tests 13 648 :white_check_mark: 544 :zzz: 0 :x: 14 588 runs  14 028 :white_check_mark: 560 :zzz: 0 :x:

Results for commit 43759900.