GH-128520: Divide pathlib ABCs into three classes

[barneygale]

In the private pathlib ABCs, rename PurePathBase to JoinablePath, and split PathBase into ReadablePath and WritablePath. This improves the API fit for read-only virtual filesystems.

The split of PathBase entails a similar split of CopyWorker (implements copying) and the test cases in test_pathlib_abc.

In a later patch, we'll make WritablePath inherit directly from JoinablePath rather than ReadablePath, which will help with write-only filesystems. For a couple of reasons, this isn't quite possible yet.

• Issue: Make pathlib ABCs usable by zipfile.Path #128520

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Fedora Stable Refleaks 3.x has failed when building commit 22a4421.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/123/builds/536) and take a look at the build logs.
4. Check if the failure is related to this commit (22a4421) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/123/builds/536

Failed tests:

• test.test_multiprocessing_forkserver.test_processes

Test leaking resources:

• test_processes: memory blocks
• test_processes: references

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 21, done.        
remote: Counting objects:   4% (1/21)        
remote: Counting objects:   9% (2/21)        
remote: Counting objects:  14% (3/21)        
remote: Counting objects:  19% (4/21)        
remote: Counting objects:  23% (5/21)        
remote: Counting objects:  28% (6/21)        
remote: Counting objects:  33% (7/21)        
remote: Counting objects:  38% (8/21)        
remote: Counting objects:  42% (9/21)        
remote: Counting objects:  47% (10/21)        
remote: Counting objects:  52% (11/21)        
remote: Counting objects:  57% (12/21)        
remote: Counting objects:  61% (13/21)        
remote: Counting objects:  66% (14/21)        
remote: Counting objects:  71% (15/21)        
remote: Counting objects:  76% (16/21)        
remote: Counting objects:  80% (17/21)        
remote: Counting objects:  85% (18/21)        
remote: Counting objects:  90% (19/21)        
remote: Counting objects:  95% (20/21)        
remote: Counting objects: 100% (21/21)        
remote: Counting objects: 100% (21/21), done.        
remote: Compressing objects:  10% (1/10)        
remote: Compressing objects:  20% (2/10)        
remote: Compressing objects:  30% (3/10)        
remote: Compressing objects:  40% (4/10)        
remote: Compressing objects:  50% (5/10)        
remote: Compressing objects:  60% (6/10)        
remote: Compressing objects:  70% (7/10)        
remote: Compressing objects:  80% (8/10)        
remote: Compressing objects:  90% (9/10)        
remote: Compressing objects: 100% (10/10)        
remote: Compressing objects: 100% (10/10), done.        
remote: Total 11 (delta 8), reused 3 (delta 1), pack-reused 0 (from 0)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
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HEAD is now at 22a442181d5 GH-128520: Divide pathlib ABCs into three classes (#128523)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)

make: *** [Makefile:2298: buildbottest] Error 2