Reinvestigate reusing TxState across transactions

This issue tracks reimplementing the work from stale PR #3831, which has been closed because it is too far out of date to merge directly.

Original pull request

• PR #3831: Reuse TxState, stashing in CommittedState btw txes
• Original author: @Centril

What the original PR was trying to do

Description of Changes See tin. API and ABI breaking changes None Expected complexity level and risk 2 Testing TODO

Closure context

• I'm closing this because we did not find that this substantially improved performance, although it should be noted that we now have new information and that this should perhaps be reinvestigated. That reinvestigation will be tracked by a new ticket.

Reimplementation notes

• Reimplement this work on top of current master in a new PR.
• Keep the original PR linked as historical context and as a source of useful implementation ideas where still relevant.

Start by reviewing the historical implementation and discussion in PR #3831, then inspect the current transaction-state code on master to identify what remains applicable. Reimplement the approach in a new PR and verify whether it provides a meaningful performance improvement; testing requirements are not specified in the issue.