fix: accept numeric-string OAuth lifetime fields so refresh stops running every poll (#178)

[Percy2Live]

Problem (issue #178, point 1)

The reporter confirmed on 1.0.1 that auth.tokenJson after a successful poll contains expires_in as a string ("3600"), with no created_at/expires_at.

normalizeToken() in bluetti-stored-token-provider.js only accepted the numeric OAuth fields when typeof value.<field> === "number". A string expires_in was therefore:

• dropped by the guarded assignment, yet
• copied through the ...value spread unnormalized, and
• never used to stamp created_at (the Token expiry not parsed from BLUETTI response → refresh runs on every poll #46 receipt-time stamp also requires typeof token.expires_in === "number").

Result: no expiry is computable → isNearExpiry() defaults to true → a token refresh runs on every poll, defeating the #46 fix.

Fix

• New setFiniteNumber() helper coerces numeric strings for expires_at / expires_in / created_at, and deletes the key when the value is non-finite so the raw string can't leak through the spread into serialization.
• No fallback lifetime — matches the reporter's recommendation; the receipt-time created_at stamp now fires for the real BLUETTI shape.

Tests

• expires_in as a numeric string → token reused across several polls, zero refreshes.
• non-numeric expires_in → dropped, not serialized, no bogus created_at.

npm run check green, full token-provider suite passing.

Closes #178.