refactor: deduplicate block validation state catcher #36389

As mentioned in #34644 (review) and #35675 (review), the validation state catchers were defined in the block template manager, submitblock rpc and mining test helpers, even though they do the same thing.

Moved this helper into node/block_validation_state_catcher.h and reuse it across all three callers. An optional validation state replaces the separate found flag where used, preserving each caller's registration and result handling

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36389.

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Reviews

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #36356 _{<img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36356.svg">} (mining: move getblocktemplate cache into BlockTemplateManager by w0xlt)
• #35671 _{<img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/35671.svg">} (mining: add TxCollection to bandwidth-efficiently validate external block templates by Sjors)
• #33922 _{<img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/33922.svg">} (mining: add getMemoryLoad() and track template non-mempool memory footprint by Sjors)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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LLM Linter (✨ experimental)

Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

• ProcessNewBlock(block, true, true, &new_block) in src/test/util/mining.cpp

^{2026-09-30 11:50:19}

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🚧 At least one of the CI tasks failed. _{Task lint: https://github.com/bitcoin/bitcoin/actions/runs/36709743890/job/109868408911} _{LLM reason (✨ experimental): CI failed due to lint errors in src/node/block_validation_state_catcher.h—missing the required include guard and using quote-based #include instead of bracket syntax.}

<details><summary>Hints</summary>

Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

• Possibly due to a silent merge conflict (the changes in this pull request being incompatible with the current code in the target branch). If so, make sure to rebase on the latest commit of the target branch.

• A sanitizer issue, which can only be found by compiling with the sanitizer and running the affected test.

• An intermittent issue.

Leave a comment here, if you need help tracking down a confusing failure.

</details>

Concept ACK

Had opened this on the wrong branch, closing this in favor of #36469