feat: error on unrecognized fields in signer config

[brice-stacks]

The signer now refuses to start if its configuration file contains unrecognized fields, instead of silently ignoring them. This catches misspelled option names that previously would have slipped by without warning.

[coveralls]

Coverage Report for CI Build 30939477944

Coverage decreased (-0.004%) to 86.614%

Details

• Coverage decreased (-0.004%) from the base build.
• Patch coverage: 16 of 16 lines across 1 file are fully covered (100%).
• 108 coverage regressions across 29 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

108 previously-covered lines in 29 files lost coverage.

Top 10 Files by Coverage Loss	Lines Losing Coverage	Coverage
stacks-node/src/neon_node.rs	13	83.14%
stackslib/src/net/download/nakamoto/tenure_downloader_unconfirmed.rs	9	74.13%
stackslib/src/net/server.rs	9	89.17%
stackslib/src/net/download/nakamoto/download_state_machine.rs	8	89.84%
stacks-node/src/nakamoto_node/miner.rs	8	87.12%
stacks-signer/src/v0/signer_state.rs	7	92.73%
clarity/src/vm/functions/bitcoin_madhouse.rs	6	82.57%
stackslib/src/net/stackerdb/config.rs	6	81.45%
stackslib/src/chainstate/stacks/index/marf.rs	5	84.07%
stacks-common/src/deps_common/bitcoin/network/encodable.rs	4	88.71%

---

Coverage Stats

Relevant Lines:	232756
Covered Lines:	201599
Line Coverage:	86.61%
Coverage Strength:	19453472.27 hits per line

---

💛 - Coveralls

[hstove-stacks]

LGTM

[brice-stacks]

When #7492 merges, change this to a .breaking