…r warning

This refactor does not change any behavior, except for the integer
sanitizer warning.

Can be tested via:

UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./bld-cmake/bin/bitcoin-cli -stdinrpcpass uptime

Github-Pull: bitcoin#34597
Rebased-From: fa6af85

```
src/common/netif.cpp:137:51: error: comparison of integers of different signs: 'int64_t' (aka 'long') and 'unsigned long' [-Werror,-Wsign-compare]
  137 |         for (nlmsghdr* hdr = (nlmsghdr*)response; NLMSG_OK(hdr, recv_result); hdr = NLMSG_NEXT(hdr, recv_result)) {
      |                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/netlink/netlink.h:220:31: note: expanded from macro 'NLMSG_OK'
  220 | #define NLMSG_OK(_hdr, _len)            NL_ITEM_OK(_hdr, _len, NLMSG_HDRLEN, _NLMSG_LEN)
      |                                         ^                ~~~~  ~~~~~~~~~~~~
/usr/include/netlink/netlink.h:203:10: note: expanded from macro 'NL_ITEM_OK'
  203 |         ((_len) >= _hlen && _LEN_M(_ptr) >= _hlen && _LEN_M(_ptr) <= (_len))
      |           ~~~~  ^  ~~~~~
1 error generated.
```

Happens on FreeBSD 15.0, with the default compiler (Clang 19).

On FreeBSD 14, `/usr/include/netlink/netlink.h` contains:
```
 #define NLMSG_HDRLEN                    ((int)sizeof(struct nlmsghdr))
```

On FreeBSD 15, `/usr/include/netlink/netlink.h` contains:
```
 #define NLMSG_HDRLEN                    (sizeof(struct nlmsghdr))
```

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

Github-Pull: bitcoin#34093
Rebased-From: c1361fc

Github-Pull: bitcoin#34690
Rebased-From: fa48f8c

Improve dependencies.md to document IPC dependencies better:

- Link to native_capnp.mk file not capnp.mk file so it's possible to see what
  version of Cap'n Proto is being used in release binaries. This is important
  since bitcoin#31895 dropped the "Version Used" column and the capnp.mk file does not
  include version number.
- Indicate Capn"Proto is used for IPC and link to multiprocess.md documenting
  the feature.
- Link to correct PR requiring Cap'n Proto 0.7.1. Previous link was
  pointing at PR which required 0.7.0.
- Mention libmultiprocess as a dependency even though it is included as a git
  subtree and can be built as a cmake subproject. Libmultiprocess still needs
  to be built separately when cross compiling, and is useful to build separately
  when developing, and is still a depends package.

Based on 2cf352f from bitcoin#33623 by willcl-ark
which made similar changes in the 29.x branch.

Github-Pull: bitcoin#34706
Rebased-From: b87a1c2

Add validation for pubkeys in MuSig2 pubnonce and partial signature deserialization to prevent crashes with invalid curve points.

- Validate aggregate and participant pubkeys in PSBT MuSig2 fields

- Add comprehensive test coverage for invalid pubkey rejection

- Ensure proper error handling during PSBT deserialization

Github-Pull: bitcoin#34219
Rebased-From: f51665b

Github-Pull: bitcoin#34713
Rebased-From: 2a7a4f6

The `fee` field in the `getblock` RPC result (verbosity 2 and 3) may be
omitted when block undo data is not available. Marking it optional in
the `RPCResult` aligns the documented schema with the runtime behavior.

Github-Pull: bitcoin#34702
Rebased-From: f580cc7