Allow adding nickname delimiter patterns at runtime

[derek73]

Summary

• Fixes the "adding a regex at runtime has no effect" half of Dynamic changes #112: parse_nicknames() looped over a hardcoded tuple of three named regexes, so overriding an existing pattern in CONSTANTS.regexes and re-parsing already worked, but there was no way to add a new delimiter pattern.
• Constants now exposes nickname_delimiters, a named TupleManager of delimiter patterns (seeded with the existing quoted_word/double_quotes/parenthesis regexes), and parse_nicknames() iterates it instead of a literal tuple.
• Add a new pattern under a new key (hn.C.nickname_delimiters['curly_braces'] = re.compile(...)) and call parse_full_name() again to pick it up — no subclassing or monkeypatching required.
• Docs updated (docs/customize.rst) with a worked example.

Test plan

• New test test_add_custom_nickname_delimiter in tests/test_nicknames.py reproduces the runtime-add scenario from the issue thread
• Full suite passes: 982 passed, 4 skipped, 22 xfailed
• Verified pickling/deepcopy still round-trip the new attribute correctly

Closes #112 (the nickname-delimiter case discussed in the thread; further generalization to other config groups mentioned in the issue is left as future work if a concrete need comes up).

🤖 Generated with Claude Code

[derek73]

Ran a multi-agent review pass (code, tests, comments) on the original commit and it caught a real regression before merge, now fixed in the second commit:

Critical bug found: the original approach snapshotted quoted_word/double_quotes/parenthesis into a new nickname_delimiters dict at Constants.__init__ time. That silently broke the pre-existing, documented customization path — overriding CONSTANTS.regexes.parenthesis and calling parse_full_name() again — because the snapshot never saw later changes to regexes. Verified directly: worked on master, broken on the first commit here.

Fix: parse_nicknames() now reads the three built-ins live from self.C.regexes (restoring that override path), and additionally iterates a renamed, initially-empty extra_nickname_delimiters collection for genuinely new patterns — matching what #112 actually asked for (add a pattern, don't have to replace one).

Also addressed from review:

• extra_nickname_delimiters was missing from tests/conftest.py's autouse snapshot/restore list, so a test mutating the global CONSTANTS copy would have leaked state into later tests — added.
• Added a removal test, a regression test for the override path, a pickle round-trip assertion, and a test confirming the suffix/nickname disambiguation logic in handle_match() applies uniformly through a custom delimiter, not just the three built-ins.
• Fixed the now-stale parse_nicknames() docstring.

Full suite: 990 passed, 4 skipped, 22 xfailed.