wallet: report importdescriptors timestamp errors per item #35272

Fixes #35181.

Missing or invalid timestamp values in importdescriptors now return an error in the matching result entry instead of aborting the whole RPC. Valid entries in the same batch can still be imported.

Tests:

• ninja -C build bitcoind bitcoin-cli test_bitcoin
• test/functional/wallet_importdescriptors.py --configfile=$PWD/build/test/config.ini
• build/bin/test_bitcoin -t wallet_rpc_tests
• python3 -m py_compile test/functional/wallet_importdescriptors.py
• git diff --check

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35272.

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NACK

There has been three PRs in the lasts days addressing the same issue. This comment applies here too: #35185 (comment)