Added support for URL decoding of the search parameter for pages

[yzcheung]

Here’s a structured PR description following the format you provided:

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Description of this PR

This PR adds support for URL decoding of the search parameter in pages mode. The changes ensure that URL-encoded characters in the search parameter are properly decoded, improving the handling of query strings in pages mode.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Implement URL decoding for the search parameter in pages mode
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLs as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

This structure aligns with the given format and provides clear documentation of the changes.

[yzcheung]

This PR aims to correctly parse query parameters after URL encoding for pages.
eg: "%3fquery%3dsomething" should be decoded as {'query': 'something'}.

[T4rk1n]

Looks good, just missing a changelog entry.