test(keymaster): cover WalletSQLite defaults and connection guards

[macterra]

Result

	before	after
db/sqlite.ts branches	53.8% (7/13)	100% (13/13)
db/sqlite.ts lines	93.1%	100%
repo branches	86.46%	86.68%

4 tests. 2,066 passing, eslint clean. Test-only.

A real asymmetry, surfaced by covering the default arguments

The two wallet backends implement the same interface but differ on folder creation:

// WalletJson.saveWallet
if (!fs.existsSync(this.dataFolder)) {
    fs.mkdirSync(this.dataFolder, { recursive: true });
}

// WalletSQLite.connect — no equivalent
this.db = await open({ filename: this.walletName, driver: sqlite3.Database });

WalletSQLite opens ${dataFolder}/${file} directly, so an absent directory fails with a raw SQLITE_CANTOPEN rather than being created, or reported with a message that says what is wrong.

The existing tests never hit this because they always pass an already-created temp dir. Only the default-argument path exposes it — which is precisely the branch that was uncovered, so the gap in coverage and the gap in behaviour were the same gap.

Pinned by test asserting current behaviour rather than changed. Whether two implementations of one interface should agree here is a design call, not something to decide inside a coverage PR. Practically: a fresh deployment using the sqlite wallet needs data/ to exist beforehand. The Docker images likely provide it via a volume mount, so this may never have bitten anyone.

The other branches

Four unexercised default parameters (walletFileName and dataFolder, on both the constructor and create()), and the two defensive !this.db guards — reachable only by stubbing connect() to a no-op, since a successful connect always sets the handle. That is noted in a comment so the next reader knows the guard is otherwise dead code.

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