fix: align the fast parser with the default parser

[chuanghiduoc]

Follow-up to #1043. Aligns the fast parser with the default parser on all three divergence classes from the issue.

Changes

1. Quoted value starting on a later line after KEY=

The default regex's quoted alternative carries a greedy leading \s* that crosses newlines, so a quote on a later line is consumed as the value. The scanner now detects when a newline was crossed after the separator and, if the next non-blank char is a quote, parses the value with full multiline support:

require('dotenv').parse('A=\n\n"hello\nworld"', { fast: true })
// before: { A: '' }
// after:  { A: 'hello\nworld' }   (matches default)

Junk after the closing quote on that line still kills the whole alternative (the raw fallback cannot cross newlines), matching A=\n\n"x" junk → { A: '' }.

2. \f, \v, U+00A0 before a key

Added to the whitespace-skip set alongside space/tab/newline/BOM:

parse('\u00A0A=1', { fast: true })
// before: {}
// after:  { A: '1' }

3. Trailing junk after a closing quote

TOKEN="abc" oops now keeps the raw single-line value "abc" oops (the quoted form only survives when nothing but spaces/tabs or a comment follows the closing quote — anything else makes the raw [^\r\n#]+ fallback take over starting at the opening quote, exactly like the regex backtracks).

Tests

• tests/test-fast-parity.js — parity assertions for the three issue cases; failed on master (5 fail), passes now.
• Existing test-parse-fast.js cross-checks against tests/.env and the multiline fixture: failed on master, passes with this change.

Full suite on Windows: 201 total / 197 pass / 3 skip-adjacent fails — the 3 remaining failures (deals with file:// path, displays the injected env message without tips) are pre-existing environment failures that also fail on unmodified master.