Adds postprocessor to track time step number for transient problems

Minor quality-of-life improvement for users who want to track
time step counts during their MOOSE simulations.

closes #29127

framework/doc/content/source/postprocessors/NumTimeSteps.md

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+# TimestepSize
+
+!syntax description /Postprocessors/NumTimeSteps
+
+## Description
+
+`NumTimeSteps` reports the timestep size.
+
+## Example Input Syntax
+
+!listing /Users/achaube/tools/moose/test/tests/postprocessors/num_time_steps/moose.i block=Postprocessors
+
+!syntax parameters /Postprocessors/NumTimeSteps
+
+!syntax inputs /Postprocessors/NumTimeSteps
+
+!syntax children /Postprocessors/NumTimeSteps

framework/include/postprocessors/NumTimeSteps.h

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+//* This file is part of the MOOSE framework
+//* https://www.mooseframework.org
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#pragma once
+
+#include "GeneralPostprocessor.h"
+
+class NumTimeSteps : public GeneralPostprocessor
+{
+public:
+  static InputParameters validParams();
+
+  NumTimeSteps(const InputParameters & parameters);
+
+  virtual void initialize() override {}
+  virtual void execute() override {}
+
+  /**
+   * This will return the current time step number.
+   */
+  virtual Real getValue() const override;
+
+protected:
+  FEProblemBase & _feproblem;
+};

framework/src/postprocessors/NumTimeSteps.C

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+//* This file is part of the MOOSE framework
+//* https://www.mooseframework.org
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#include "NumTimeSteps.h"
+#include "FEProblem.h"
+
+registerMooseObject("MooseApp", NumTimeSteps);
+
+InputParameters
+NumTimeSteps::validParams()
+{
+  InputParameters params = GeneralPostprocessor::validParams();
+  params.addClassDescription("Reports the timestep number");
+  return params;
+}
+
+NumTimeSteps::NumTimeSteps(const InputParameters & parameters)
+  : GeneralPostprocessor(parameters), _feproblem(dynamic_cast<FEProblemBase &>(_subproblem))
+{
+}
+
+Real
+NumTimeSteps::getValue() const
+{
+  return _feproblem.timeStep();
+}

test/tests/postprocessors/num_time_steps/gold/moose_out.csv

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+time,timestep_ctr
+0,0
+1,1
+2,2
+3,3
+4,4
+5,5
+6,6
+7,7
+8,8
+9,9
+10,10

test/tests/postprocessors/num_time_steps/moose.i

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+[Mesh]
+  type = GeneratedMesh
+  dim = 3
+  nx = 30
+  ny = 30
+  nz = 30
+[]
+
+[Variables]
+  [temperature]
+    initial_condition = 500.0
+  []
+[]
+
+[AuxVariables]
+  [source]
+  []
+[]
+
+[Kernels]
+  [conduction]
+    type = HeatConduction
+    variable = temperature
+  []
+  [source]
+    type = CoupledForce
+    variable = temperature
+    v = source
+  []
+[]
+
+[AuxKernels]
+  [source]
+    type = ParsedAux
+    variable = source
+    function = 'temperature*7*t'
+    coupled_variables = 'temperature'
+    execute_on = 'linear'
+    use_xyzt = true
+  []
+[]
+
+[BCs]
+  [left]
+    type = DirichletBC
+    variable = temperature
+    boundary = 'left'
+    value = 500.0
+  []
+  [right]
+    type = DirichletBC
+    variable = temperature
+    boundary = 'right'
+    value = 600.0
+  []
+  [top]
+    type = DirichletBC
+    variable = temperature
+    boundary = 'top'
+    value = 650.0
+  []
+  [front]
+    type = DirichletBC
+    variable = temperature
+    boundary = 'front'
+    value = 650.0
+  []
+[]
+
+[Materials]
+  [k]
+    type = GenericConstantMaterial
+    prop_names = 'thermal_conductivity'
+    prop_values = '1.5'
+  []
+[]
+
+[Postprocessors]
+  [timestep_ctr]
+    type = NumTimeSteps
+  []
+[]
+
+
+[Executioner]
+  type = Transient
+  nl_abs_tol = 1e-10
+  nl_rel_tol = 1e-4
+  dt = 1
+  num_steps = 10
+[]
+
+[Outputs]
+  exodus = false
+  csv = true
+  hide = 'source temperature'
+[]
+

test/tests/postprocessors/num_time_steps/tests

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+[Tests]
+  [num_time_steps]
+    type = 'CSVDiff'
+    input = 'numtimesteps.i'
+    csvdiff = 'numtimesteps_out.csv'
+    requirement = 'The postprocessor `NumTimeSteps` shall count the number of time-steps accurately'
+                   'over the course of a transient solve'
+  []
+[]