Incorrect parsing of timestamp passing as string

**Describe the bug**
dayjs returns some big negative number instead of actual timestamp when passing it as string to `dayjs`. `dayjs(1762232987879).valueOf()` -> `1762232987879` correct.
`dayjs("1762232987879").valueOf()` -> `-6503275387000` incorrect.
This behaviour lead to incorrect future formatting, returning a date with 1730 year, and also incorrect work for `isBefore` and `isAfter`.

**Expected behavior**
`dayjs(1762232987879).valueOf()` -> `1762232987879`
`dayjs("1762232987879").valueOf()` -> `1762232987879`

**Information**
- Day.js Version 1.11.19
- OS: macOS 15.7.1
- Browser Chrome Version 142.0.7444.60 (Official Build) (x86_64) / Jest / Vitest
- Time zone: any

Start by running the reported dayjs(...) examples in the repository's test environment and trace the timestamp-string parsing path. Compare numeric and string inputs, including the resulting valueOf(), isBefore, and isAfter behavior. Done means the string timestamp matches the numeric timestamp without producing the incorrect 1730 date.

Written by the indexing model from the issue text.