[PWGCF] Add hist to calculate v22 - deltaPt

[huinaibing]

• Add a new function to calculate $\langle v_2^2\rangle - \delta p_T / \langle[p_T]\rangle$
• Add hists to calculate unidentified particles (charged but not pi ka pr) $\rho$

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 9 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 56ae29e at 2026-08-13 14:12:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 1 errors and 0 warnings.'
Found 1 errors and 0 warnings.
++ [[ 1 -gt 0 ]]
++ cat /sw/BUILD/8757076e09606a48ae8a4815b570790951e36f73/O2Physics-code-check/errors.txt
PWGCF/Flow/Tasks/pidFlowPtCorr.cxx:1662:5: error: uninitialized record type: 'bins' [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 1 -gt 0 ]]
++ exit 1
--

Full log here.

[alibuild]

Error while checking build/O2Physics/code-check for c963572 at 2026-08-13 18:08:

## sw/BUILD/O2Physics-latest/log
c++: fatal error: Killed signal terminated program cc1plus
c++: fatal error: Killed signal terminated program cc1plus
ninja: build stopped: subcommand failed.

Full log here.