storage controller: refactor non-mutable members up into Service

[jcsp]

result_tx and compute_hook were in ServiceState (i.e. behind a sync mutex), but didn't need to be.

Moving them up into Service removes a bunch of boilerplate clones.

While we're here, create a helper Service::maybe_reconcile_shard which avoids writing out all the &self. arguments to TenantState::maybe_reconcile everywhere we call it.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2496 tests run: 2376 passed, 0 failed, 120 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_vm_bit_clear_on_heap_lock: release

Code coverage* (full report)

• functions: 28.8% (7033 of 24444 functions)
• lines: 47.6% (43451 of 91295 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
b0e7e05 at 2024-03-11T14:27:07.223Z :recycle:}