fix lalpulsar doxygen header pages

@karl-wette some things seems to have broken at some point with doxygen rendering. Here's a potential fix to one issue, I'll report others separately.

This one is about some "header" pages being mostly blank, showing just the group info and nothing about function prototypes etc:

• https://lscsoft.docs.ligo.org/lalsuite/lalpulsar/group___fstatistic_tools__h.html
• https://lscsoft.docs.ligo.org/lalsuite/lalpulsar/group___transient_c_w__utils__h.html
• https://lscsoft.docs.ligo.org/lalsuite/lalpulsar/group___sin_cos_l_u_t__h.html
• https://lscsoft.docs.ligo.org/lalsuite/lalpulsar/group___compute_fstat__h.html (shows at least submodules, but missing the rest too)

This seems to be an issue with // @{ type markup. In the first commit, I started changing that and the group info to * (because I just compared to other pages that still look correct, e.g. https://lscsoft.docs.ligo.org/lalsuite/lalpulsar/group___line_robust_stats__h.html and noticed that those used that syntax). But then I found other files that use /// for the group info and still look fine, so I realised that a minimal // @{ -> /// @{ change was already sufficient (example in second commit).

Do you have a preference for the minimal change, or to use the opportunity to standardise on one format?

Also if we want to standardise more, also sometimes the group info block comes before macros and #includes, sometimes after. That doesn't have an impact I think, but might help maintenance to standardise too.