fix(doc): properly handle indentation in multi-line doc comments

[CreeptoGengar]

Fix incorrect indentation handling in documentation comment extraction.
The previous implementation only removed a single space after comment markers, which caused issues with multi-line comments having varying indentation levels.
Now the code finds the minimum common indentation across all lines in a comment block and removes it uniformly, preserving
relative alignment within the block.

[reviewable-StarkWare]

This change is 

[orizi]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @CreeptoGengar)

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a discussion (no related file):
would suggest adding a test to show the improvement.

[CreeptoGengar]

Added a test case for the indentation fix.
It covers multi-line doc comments with varying indentation levels and verifies that the minimum common indentation is correctly removed while preserving relative alignment between lines.

[orizi]

@orizi reviewed all commit messages.
Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @CreeptoGengar and @FroyaTheHen)

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a discussion (no related file):
@FroyaTheHen

[FroyaTheHen]

Reviewable status: 0 of 3 files reviewed, 3 unresolved discussions (waiting on @CreeptoGengar and @orizi)

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crates/cairo-lang-doc/src/tests/test-data/indentation.txt line 1 at r2 (raw file):

//! > Documentation

Can you please add a test case that would have failed before but now passes?

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crates/cairo-lang-doc/src/tests/test-data/indentation.txt line 43 at r2 (raw file):

This line has extra indentation.
This line has less indentation.
Another indented line.

I understand that the behaviour expected from those changes would be to preserve the indentation in a way that would remove the number of leading whitespaces common to all the comment lines. (Please argue otherwise if you do not agree.) Although the test shows all of the leading whitespaces are removed. Isn't the expected 👇 ??

Suggestion:

//! > Item documentation #2
Function with multi-line doc comment.
    This line has extra indentation.
  This line has less indentation.
    Another indented line.