* feat: allow extension blocks to break a Paragraph

currently the list of elements that can break a Paragraph is hardwired in the Paragraph implementation.

This PR suggests a new BlockElement property `breaks_paragraph` that allows extensions to define blocks that can also break a paragraph without the need to override the Paragraph `break_paragraph` implementation.

* refactor: improve test

* Apply suggestions from code review

refactor: method return types

Co-authored-by: Frost Ming <mianghong@gmail.com>

---------

Co-authored-by: Frost Ming <mianghong@gmail.com>

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

…ixes #257

Signed-off-by: Frost Ming <me@frostming.com>

* Remove unused type: ignore directives

* Force using types for objprint

* Add types for pygments

* Fix type-arg typing errors

* Fix redundant-cast typing errors

* Fix NameError in tests

CommonMark §2.3 ("Insecure characters") requires that literal U+0000
code points in source be replaced with U+FFFD. Marko's entity-reference
path already honours this for � / �, but literal NULs in the
input were passed straight through to text, code spans, and code blocks.

Add the substitution to _preprocess_text so that all parser/renderer
paths see a sanitised buffer. Add regression tests covering NUL in
plain text, code spans, and fenced code blocks.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Make _RendererDispatcher fully generic

By making _RendererDispatcher and the RendererFunc type fully generic,
the render_dispatch decorator can be strongly typed. This eliminates mypy
typing errors on method using render_dispatch or _RendererDispatcher,
provided the method is correctly typed.

* Those were there for a reason

Signed-off-by: Frost Ming <me@frostming.com>