Add timer for walker log

[PDoakORNL]

Proposed changes

I was curious about the cost of walker logging so I added a timer.
Running the batched energy density with it on its 100 times more expensive than the energy denisty but still just ~15% of the total dmc time.
This is wth 2400 walkers across 8 ranks with 3 crowds each. 8 v100's
diamond 1x1x1

What type(s) of changes does this code introduce?

Delete the items that do not apply

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

dgx server

Checklist

Update the following with a yes where the items apply. If you're unsure about any of them, don't hesitate to ask. This is
simply a reminder of what we are going to look for before merging your code.

• Yes/No. This PR is up to date with current the current state of 'develop'
• Yes/No. Code added or changed in the PR has been clang-formatted
• Yes/No. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• Yes/No. Documentation has been added (if appropriate)

[ye-luo]

This PR adds only 1 walker_log timer covering all kinds of walker_log operations. Only the total time can be interpreted and time per call is not really meaningful.
Could you put fine timers into functions of WalkerLogCollector and WalkerLogManager? In this way, we will have better timer resolution and zero timer impact if walker_log is not activated.

[PDoakORNL]

The timer gets listed in different enclosing timer scopes in the output. It's quite easy to tell what is what from the number of calls for each timer output. But I get what you mean, will do when I have time.

[prckent]

Agreeing with Ye's suggestions: Better to have the logging within the log manager etc. Also nicer to have finer timers in case any one operation is particularly slow.