fix: generate public API docs correctly

[zhjwpku]

No description provided.

[zhjwpku]

This patch resolves the following doc issues:

[manuzhang]

are these comments required for this fix?

[zhjwpku]

I guess so. If not for this comment on the header files, the header would be listed but wouldn't be clickable， see https://cpp.iceberg.apache.org/api/files.html

[manuzhang]

The Doxygen config still scans implementation .cc files, so internal implementation helpers can remain in the public API docs.

[zhjwpku]

The Doxygen config still scans implementation .cc files, so internal implementation helpers can remain in the public API docs.

Good catch, I have changed FILE_PATTERNS to include only *.h *.md *.dox, hope this works.

[wgtmac]

Nice! Thanks @zhjwpku for fixing this and @manuzhang for the careful review!