Fix pg array parsing dropping backslashes in quoted elements

[eeshsaxena]

What / Why

parsePgArrayValue unescapes a quoted Postgres array element with .replace(/\\/g, ''), which strips every backslash. That is right for an escaped quote (\" → ") but wrong for an escaped backslash (\\ should become a single \, not be removed). So a text[] / varchar[] value containing a backslash is corrupted on read.

Postgres doubles backslashes in its array output, so:

-- stored value is the string  a\b
select array['a\b']::text[];   -- wire format: {"a\\b"}

Reading that back through Drizzle today:

table.col.mapFromDriverValue('{"a\\\\b"}')            // => ['ab']            ❌ (should be ['a\b'])
table.col.mapFromDriverValue('{"c:\\\\temp\\\\x"}')   // => ['c:tempx']       ❌ (should be ['c:\temp\x'])

Any array value with a backslash is affected: Windows paths, regex patterns, LaTeX, escape sequences, etc.

Fix

Unescape with .replace(/\\(.)/g, '$1') so a backslash escapes the following character. This is the inverse of what makePgArray produces (it escapes \ → \\ and " → \") and matches how Postgres formats array output.

• Escaped backslashes now round-trip: {"a\\b"} → ['a\b'].
• Escaped quotes are unchanged: {"a\"b"} → ['a"b'] (already covered by existing tests, still green).

Added tests for escaped backslashes and for a value containing both an escaped backslash and an escaped quote.

Testing

I verified the fixed parsePgArrayValue/parsePgNestedArray against every existing parsePgArray test input (all still pass) plus the new backslash cases. I wasn't able to spin up the full monorepo test run locally (slow dependency install in my environment), so I'd appreciate CI running the parsePgArray suite.

[eeshsaxena]

Worth flagging the blast radius: this hits any array column whose values can contain a backslash, so Windows paths, regex patterns, and escape sequences in a text[] silently lose data on read, and it is a read-path corruption rather than a crash so it can go unnoticed. The fix is a one-character-class change to the unescape and it leaves the escaped-quote handling and all existing tests untouched.