tests: raise wallet coverage from 77.7% to 84.4%

[TeoSlayer]

Summary

• Adds targeted tests for previously-uncovered paths in pkg/wallet, pkg/walletipc, pkg/evm, and cmd/wallet.
• Production code is unchanged — only new *_test.go files.
• Total module coverage: 77.7% -> 84.4% (+6.7pp), clearing the 80% target.

Per-package gains

Package	Before	After
pkg/wallet	74.1%	85.5%
pkg/walletipc	82.1%	86.2%
pkg/evm	82.4%	84.1%
cmd/wallet	76.3%	76.3%

What's covered now

• Wallet.HookPreSendMessage (paywall happy path + every error branch: missing peer, bad base64 data, bad spec, blank spec, no-paywall passthrough, custom method/escrow IDs).
• Wallet.HookPostRecvMessage (no-data, bad-base64, bad-json, incomplete-envelope passthroughs + happy-path roundtrip with the sender's pre-send output).
• Wallet.Request and Wallet.Topup validation branches (zero amount, empty asset, missing source / expiresIn).
• sqliteStore.GetIssued and sqliteStore.IsSettled (previously 0% — only the memory store had tests).
• walletipc dispatcher: history Since/Before time-bounds, empty-payload decode, type-mismatched JSON, ExpiresInSeconds=0 rejection.
• evm.EVMMethod accessors (ID, ChainID, Token, Address), Client.Endpoint, NewClient(_, nil) default-http branch, and Uint128 packing.

Safety

• All file-based tests use t.TempDir() — nothing touches ~/.pilot.
• No t.Logf / fmt.Println of any private-key bytes (seed, signature, or otherwise) in any new test file.

Test plan

• go test -race -count=1 -timeout 120s ./... — all pass
• go vet ./... — clean
• go test -coverprofile=/tmp/wallet-after.cov -count=1 ./... then go tool cover -func=... | tail -1 — confirms 84.4%

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