Implement parsing of conditions

[nforro]

Statements such as %if, %else and %endif are currently treated as regular section content.
That can cause issues, especially with conditions spanning across multiple sections - if a section is deleted, modified or moved, it can lead to syntax errors as the condition block could be broken apart.
Figure out how to deal with this.

[lachmanfrantisek]

Still relevant. Let us know if you need this (either in Specfile or for Packit).

[xsuchy]

I am hitting this when parsing amavis.spec. I get this TB

Traceback (most recent call last):
  File "/home/msuchy/projects/license-validate/./convert-spec-universal.py", line 65, in <module>
    with specfile.tags(section) as tags:
         ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/msuchy/.local/lib/python3.12/site-packages/specfile/context_management.py", line 133, in __call__
    self.values[key] = next(self.generators[key])
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/msuchy/.local/lib/python3.12/site-packages/specfile/specfile.py", line 292, in tags
    tags = Tags.parse(section, context=self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/msuchy/.local/lib/python3.12/site-packages/specfile/tags.py", line 497, in parse
    lines = process_conditions(list(section), macro_definitions, context)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/msuchy/.local/lib/python3.12/site-packages/specfile/conditions.py", line 133, in process_conditions
    result.append((line, branches[-2]))
                         ~~~~~~~~^^^^
IndexError: list index out of range