Fix check_style.sh regex patterns to properly detect style issues

[r0qs]

While working on #16266, I noticed that some style issues were not being caught by our script. This PR fixes issues in check_style.sh that were causing:

1. grep warnings due to invalid or unnecessary regex syntax when using the Extended Regular Expressions (-E) option
2. Real style violations being incorrectly excluded from detection

The old patterns ^* [*] and ^*//.* were flagged as invalid regex by grep (i.e., * at start of expression) and inadvertently matched any line containing * (space followed by asterisk). This caused real pointer alignment issues like CFGNode *_node to be excluded from detection.

The new pattern :[0-9]+:\s*\*\s only excludes comment continuation lines (where the source starts * followed by whitespace), allowing real style violations to be properly detected.

I also changed \/(\/|\*) to /[/*]. Forward slashes are not special characters in regular expressions and do not need escaping. The unnecessary escaping was causing grep: warning: stray \ before / to appear in the script output.

[r0qs]

I think this PR highlights the fragility of our current regex-based approach to style checking. The patterns were silently broken, causing real violations to go undetected while producing confusing warnings. This approach is inherently error-prone and difficult to maintain.

This is another reason to reconsider adopting clang-format as proposed in #15226. While there are differing opinions among team members about specific formatting choices, having an automated and reliable solution is preferable to maintaining brittle regex patterns that can fail silently.

[cameel]

This is another reason to reconsider adopting clang-format as proposed

There is nothing to reconsider. We already agreed that we want to switch to an automatic formatter when that's good enough to give us something reasonably close to our (Rust-like) style. Last time we checked, clang-format was too Google-style-centric and the results were not satisfactory. But there were patches going in and the situation was supposedly improving so it could be better now. IIRC someone from the team volunteered to try to check it again.

Looks like no progress since then though, which I guess is understandable given that this is far from being a priority and for the last half year+ we've been severely understaffed. But still, there's nothing to decide here. Someone just has to do it.

This approach is inherently error-prone and difficult to maintain.

It's fine for what it is IMO. It's not meant to be a full style-checker. It just catches low-hanging fruit. TBH I would have expected there to be far more breakage here given that we pretty never touch it. It may be difficult to maintain but we cannot honestly say we're really maintaining it :P We're just letting it rot because everyone is looking forward to a formatter.

[clonker]

There is nothing to reconsider.

We might consider just switching styles to something supported.

IIRC someone from the team volunteered to try to check it again.

That was me, a while ago, couldn't get it to match our style though.

Someone just has to do it.

Someone can look into it again but really I think we should be focusing more on code and less on style.

We're just letting it rot because everyone is looking forward to a formatter.

Let's use one, then? :)