Draft: [hiopy] Subtasks

Creating subtasks for the flush operation in hiopy.

Needs some further testing...

added hiopy label

assigned to @k202160

added 9 commits

• 0fe729df...fad71204 - 5 commits from branch main
• 3546e3c0 - feat: add possibility to add subtsaks to taskqueue
• 34dac4af - feat: submit flush in hiopy as separate task
• b44ce405 - fix: avoid deconstruction of std::function in tsqueue
• 40e8c240 - fix: capture t explicitly in flush task

Compare with previous version

added 25 commits

• 40e8c240...24469dce - 21 commits from branch main
• 7b73e142 - feat: add possibility to add subtsaks to taskqueue
• a5e7be0c - feat: submit flush in hiopy as separate task
• ca6280c4 - fix: avoid deconstruction of std::function in tsqueue
• 5353420f - fix: capture t explicitly in flush task

Compare with previous version