sync.h is low-level and should not require any other subsystems.

Move the lone remaining logging call to the .cpp. Any cost incurred by an
additional function call should be trivial compared to the logging itself.

Currently arguments passed through the validation interface are copied
three times. Once on capture in the event, again when the event itself
is copied into the task runner lambda, and when the various arguments
used by the logging statement are copied into the lambda.

This change avoids the variables captured by the event being copied
again. Next to avoiding needless copies, this is done in preparation of
the following two commits, which seek to clarify the ownership semantics
of the blocks passed through the validation interface.

Co-authored-by: stickies-v <stickies-v@protonmail.com>

This makes existing behaviour of the block's destructor triggering on
the scheduler thread more explicit by moving it to the thread. The
scheduler thread doing so is useful, since it does not block the thread
doing validation while releasing a block's memory.

Previously, both the caller and the queued event lambda held copies of
the shared_ptr. The block would typically be freed on the scheduler
thread - but only because it went out of scope before the queued event
on the scheduler thread ran. If the scheduler ran first, the block would
instead be freed on the validation thread.

Now, ownership is transferred at each step when invoking the
BlockConnected signal: connected_blocks yields via std::move,
BlockConnected takes by value, and the event lambda move-captures the
shared_ptr. Though it is possible that this only decrements the block's
reference count, blocks are also read from disk in `ConnectTip`, which
now explicitly results in their memory being released on the scheduler
thread.

This makes existing behaviour of the block's destructor triggering on
the scheduler thread more explicit by moving it to the thread. The
scheduler thread doing so is useful, since it does not block the thread
doing validation while releasing a block's memory.

DisconnectTip already creates and destroys the block itself, so moving
it into the validation signals is well scoped.

79467e3 threading: never require logging from sync.h (Cory Fields)

Pull request description:

  This is an updated version of #34793 after stickies-v [pointed out that the approach there was broken](#34793 (comment)).

  sync.h is low-level and should not require any other subsystems.

  Move the lone remaining logging call to the .cpp. Any cost incurred by an additional function call should be trivial compared to the logging itself.

ACKs for top commit:
  stickies-v:
    re-ACK 79467e3 , thanks for doing the modernization right away 👍
  sedited:
    ACK 79467e3

Tree-SHA512: 53e4b19cbf6ec81ce6aee06092a07e56877e2247a2614a148ba25c276dc5cf00d68445f9cd43dbd71e4481da74b788e3e20d3634484760d037f94d44bf13ea9c

779e782 fuzz: wallet: add target for `MigrateToDescriptor` (brunoerg)

Pull request description:

  This PR adds fuzz coverage for the scriptpubkeyman migration (`MigrateToDescriptor`). Note that it's a test for the migration of the scriptpubkey manager, not for the whole migration process as tried in #29694, because:
  1) The wallet migration deals with DBs which is expensive for fuzzing (was getting around 3 exec/s);
  2) Mocking would require lots of refactors.

  This target loads keys, HDChain (even inactive ones), watch only and might add tons of different scripts, then calls `MigrateToDescriptor`. It does not play with encrypted stuff because it would make the target super slow. Also, after the migration there are some assertions that would work as a regression test for #31452, for example.

ACKs for top commit:
  frankomosh:
    Code Review ACK 779e782
  marcofleon:
    reACK 779e782

Tree-SHA512: 08ef5166602c21658765bc063c5421e81055d094d346c4e2a28215209c6b7768b99a424f3ba47cf718dc8d827a588da22394ba23402a40a71a976d80d65e6c2e

d6f680b validation: Move block into BlockDisconnected signal (sedited)
4d02d2b validation: Move block into BlockConnected signal (sedited)
8b0fb64 validation: Move validation signal events to task runner (sedited)

Pull request description:

  This enforces behaviour that is currently already implicit: The destructor for blocks runs mostly in the [scheduler thread](https://bitcoin-dev-tools.github.io/benchcoin/results/pr-176/20472174834/mainnet-default-instrumented-head-flamegraph.svg?x=2762391536960&y=684). The change should make it a bit clearer what the ownership semantics for these validation signals are.

  `BlockConnected` already takes a reference to a block that is emplaced in `connected_blocks`. Once `connected_blocks` is iterated through, it is not reused. Similarly `BlockDisconnected` currently takes a reference to a block that is discarded after the call to it. Note that this does not give the guarantee that blocks' lifetimes are extended by other means once they are connected. For example after IBD, the block's lifetime is extended in net_processing's `m_most_recent_block` and `ActivateBestChain` itself takes a copy of the block's shared pointer, meaning its caller may delay de-allocation.

ACKs for top commit:
  maflcko:
    re-review ACK d6f680b 🔌
  stickies-v:
    re-ACK d6f680b
  frankomosh:
    Re-ACK d6f680b

Tree-SHA512: 9209a7d23e7af0d76fa70dff958b1329f38ef29ccc49b5a32bcf9f349d59cc2bf70464ebdb130d26077c0ff9362ce9211472231d375ff1c9c89c0ec3020eac80