Remove unused headers from gsl/pointers

[knst]

• forward is already declared in utility, no need to include <algorithm> which is relatively heavy
• hash is already declared in memory, no need to bring brand-new header <system_error> for hash only.

On my machine with my customized fork of GSL it improves a compilation time of gsl/pointers drastically.

See benchmark (best time over 5 runs):

• baseline

  $ time g++ -o a.out gsl/pointers.h -O2 -g -I.
  real    0m0,572s
  user    0m0,461s
  sys     0m0,108s

• removed algorithm:

  real    0m0,505s
  user    0m0,398s
  sys     0m0,107s

• without algorithm and system_error:

  real    0m0,332s
  user    0m0,265s
  sys     0m0,067s

Considering using gsl/pointers all over codebase it speeds up compilation time of any project that uses gsl/pointers.

[beinhaerter]

I just see that std::greater<> and std::less<> are used, but <functional> is not included for them. Maybe this can be fixed, too?

[knst]

hi! Is there any chances too see a progress here? Can it get merged to the main?

it seems useful changes in my opinion.

[d-winsor]

@knst There appears to be a problem running checks on this PR. Can you push a dummy change as shown below to retrigger the tests.

commit -m "retrigger checks" --allow-empty

[knst]

@d-winsor

3 workflows awaiting approval

problem running checks on this PR

I force pushed a branch, seems as I need approval again

[PastaPastaPasta]

@knst There appears to be a problem running checks on this PR. Can you push a dummy change as shown below to retrigger the tests.

commit -m "retrigger checks" --allow-empty

Hi @d-winsor, it appears the CI is still not triggering? Please advise.

Thanks!

[PastaPastaPasta]

Hey all,

this has been approved for a while? CI failures seem unrelated? Please advise, it'd be nice to get some movement again