fix: serialize patches and deltas containing lone surrogates

[spokodev]

Problem

patch_toText (via patch_obj.toString) and diff_toDelta call encodeURI(...), which throws URIError: URI malformed on a lone (unpaired) UTF-16 surrogate.

A lone surrogate can appear even when both inputs are fully valid Unicode. Patch context-slicing (Patch_Margin, measured in UTF-16 code units) can cut between a surrogate pair, leaving one half inside a segment. So patch_make / patch_apply succeed, but serializing the resulting patch throws:

const dmp = new diff_match_patch();
dmp.patch_toText(dmp.patch_make('ab😀😀', 'b😀😀'));
// URIError: URI malformed

Fixes #22 (reported by laurent22 / Joplin).

Fix

Two helpers, encodeURISurrogateSafe and decodeURISurrogateSafe:

• For any string without lone surrogates they are byte-for-byte identical to encodeURI / decodeURI.
• A lone surrogate is additionally encoded as its WTF-8 percent byte sequence (%ED%A0-BF%80-BF). decodeURI never produces a code point in the surrogate range U+D800..U+DFFF from valid UTF-8 (it rejects those bytes as malformed), so the decoder's restore step cannot collide with any legitimate decodeURI output. Collision-safety was brute-forced over all 1.1M code points: no valid code point's encodeURI output matches the restore regex.

Four call sites swapped: the two encode sites (diff_toDelta, patch toString) and the two decode sites (diff_fromDelta, patch_fromText).

Tests

Added testLoneSurrogate (issue #22 emoji repro round-trips through patch_fromText + patch_apply; the minimal ab😀😀 to b😀😀 serialization; a diff_toDelta lone-surrogate round-trip).

Verified red before / green after: reverting only the source change makes the new test fail with URIError: URI malformed; with the fix the full suite is green. Additionally fuzzed 5000 random patch round-trips and 5000 delta round-trips mixing emoji and lone surrogates, all passing with no throws.