fix(format-url): preserve all colons in auth and encode all # in search

[suletetes]

What

Two one-line correctness fixes to formatUrl (Next's port of Node's legacy url.format), each caused by a non-global replace that only handled the first occurrence.

• Auth colons: encodeURIComponent(auth).replace(/%3A/i, ':') → /%3A/gi. The non-global flag re-decoded only the first %3A, so user:pa:ss came out as user:pa%3Ass@…. Node decodes every colon in userinfo.
• Search hashes: search.replace('#', '%23') → search.replace(/#/g, '%23'). Only the first # was encoded, so ?a=1#b#c yielded ?a=1%23b#c instead of ?a=1%23b%23c.

Why

Both diverged from Node's url.format. Verified byte-for-byte parity against Node for multi-colon (user:pa:ss, a:b:c:d), single-colon, @-in-auth, query object, multi-# search, and bare-hash inputs. The g flag only affects strings with more than one match, so single-occurrence inputs (the common case) are unchanged.

Tests

New test/unit/format-url.test.ts (7 cases), all exact toBe assertions verified against Node:

• multi-colon auth (2 and 3+ colons) regression guards
• single-colon auth, @-encoding, query object, hash normalization
• multi-# search encoding regression guard

npx jest test/unit/format-url.test.ts → 7 passed.