Keep encoded # in ZIM paths when building document URIs

[rmz-oz]

Fix #341

normalize() correctly decodes %23 to a literal # in the ZIM path, but get_document_uri() then runs that ZIM path through urlsplit(), which treats the # as a fragment delimiter and drops everything after it. So the rewritten link points to another entry, usually one that does not exist in the ZIM.

The change is one line: urlsplit(item_path.value, allow_fragments=False). A ZIM path is never encoded, so a # in it is always part of the path or query. The existing quote(relative_path, safe="/=,") then turns it back into %23. A real fragment passed as item_fragment is still appended as before.

Using @veloman-yunkan's script from openzim/overview#92 (root https://example.com/):

input	before	after
a/b%23dont_drop_me_please	a/b	a/b%23dont_drop_me_please
a/b%23x#frag (full rewrite)	a/b#frag	a/b%23x#frag
a/b?q=1%232	a/b%3Fq=1	a/b%3Fq=1%232

For comparison, urlRewriteFunction in javascript/src/wombatSetup.js already gives .../a/b%23dont_drop_me_please and .../a/b%3Fq=1%232 for the same inputs, because it goes through encodeURIComponent(). With this change the static (Python) rewriting and the dynamic (wombat) rewriting agree on these URLs.

Tests: three new cases in test_relative_url (encoded # in the path, encoded # followed by a real fragment, encoded # in the query). All three fail on main and pass with the fix. Locally: tests/rewriting/test_url_rewriting.py 139 passed; ruff check, ruff format --check and pyright on the touched files are clean. (I could not run the libmagic-dependent test modules on my machine; the rest of the suite is 627 passed before, 630 after.)

This does not touch the other points from openzim/overview#92 (#340 on //, #321 on dot segments).

CHANGELOG entry added under Unreleased / Fixed.

[benoit74]

Thank you very much, a very good PR, nothing to add besides "let's merge". Looking forward for more contribution on "sibling" issues (or any other one actually) if you see fit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7908b7b) to head (5ecd60b).

Additional details and impacted files

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##              main      #342   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           42        42           
  Lines         2694      2694           
  Branches       398       398           
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  Hits          2694      2694           

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