stdlib: Add quit and exit

[aisk]

Add quit and exit.

In CPython's REPL, there are other ways to quit or exit the REPL without calling a function (by simply typing quit or exit). These names are injected via site.py. Since GPython does not have a site.py, this REPL usage is not implemented

Close: #140

[sbinet]

LGTM

FYI, we have a little discrepancy w/ CPython (3.14) here:

$> python
>>> exit(False)
$>echo$?
0
$> python
>>> exit(True)
$>echo$?
1

compared to:

$> gpython
>>> exit(False)
False
$>echo$?
1
$> gpython
>>> exit(True)
True
$>echo$?
1

(note the extraneous printouts and the different exit codes.)

[aisk]

In CPython, bool type implemented the __index__ method, so True will be treated as 1 and False will be treated as 0 when a number like object is required. In GPython, we don't have this method implemented, thus the difference.

❯ python3
Python 3.14.3 (main, Feb 3 2026, 15:32:20) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> True.__index__()
1
>>>
gpython on  main [?] via 🐹 v1.26.0 via 🐍 v3.14.3 took 10s
❯ ./gpython
Python 3.4.0 (none, unknown)
[Gpython dev]
- os/arch: darwin/amd64
- go version: go1.26.0
>>> True.__index__()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
SystemError: 'unknown bound method type for "__index__": func() (py.Int, error)'
>>>

[aisk]

In CPython, bool type implemented the __index__ method, so True will be treated as 1 and False will be treated as 0 when a number like object is required. In GPython, we don't have this method implemented, thus the difference.

❯ python3
Python 3.14.3 (main, Feb 3 2026, 15:32:20) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> True.__index__()
1
>>>
gpython on  main [?] via 🐹 v1.26.0 via 🐍 v3.14.3 took 10s
❯ ./gpython
Python 3.4.0 (none, unknown)
[Gpython dev]
- os/arch: darwin/amd64
- go version: go1.26.0
>>> True.__index__()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
SystemError: 'unknown bound method type for "__index__": func() (py.Int, error)'
>>>

This is not correct, after #255, the behavior is still not exactly like CPython 🥲