Break apart dynamic inference step into 2 methods

[tdene]

What does this PR do ?

This PR adds no extra functionality. It only reorganizes code, by breaking async_step up into async_forward and async_bookkeep. These two methods could be run independently, but this PR does not do so: it fully preserves the pre-existing logic-flow in main, only making cosmetic changes.

BENCHMARK INFO: The "golden" benchmark returns an average value of 95.91, with expected noise of +/- 2%.
This PR seeks to not degrade the "golden" benchmark as compared to #2189. It is successful in this endeavor.

WHY IS THIS NECESSARY: This reorg is necessary for future optimizations which will run async_forward and async_bookkeep in parallel.

Contribution process

flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
        C1[Expert Review] --> C2[Final Review]
    end
    B --> C1
    C2 --> D[Merge]

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Pre-checks

• I want this PR in a versioned release and have added the appropriate Milestone (e.g., Core 0.8)
• I have added relevant unit tests
• I have added relevant functional tests
• I have added proper typing to my code Typing guidelines
• I have added relevant documentation
• I have run the autoformatter.sh on my PR

Code review

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For MRs into `main` branch

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⚠️ Only proceed to the next step once all reviewers have approved, merge-conflict are resolved and the CI is passing.
Final Review might get declined if these requirements are not fulfilled.

(Step 3): Final Review

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(Optional Step 4): Cherry-pick into release branch

If this PR also needs to be merged into core_r* release branches, after this PR has been merged, select Cherry-pick to open a new PR into the release branch.

For MRs into `dev` branch

The proposed review process for `dev` branch is under active discussion.

MRs are mergable after one approval by either [email protected] or [email protected].

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[tdene]

/ok to test 19a8f0b