fix(pg-core): prevent double JSON.parse in jsonb mapFromDriverValue (#5485)

[guoyangzhen]

Problem

The pg driver automatically parses JSON/JSONB columns using JSON.parse. When a JSONB column contains a JSON string value like "0.1", the driver returns it as the JavaScript string "0.1".

The current mapFromDriverValue in PgJsonb calls JSON.parse on all string values, which incorrectly converts JSON strings:

// Store: JSON.stringify("0.1") → DB has: "\"0.1\""
// pg driver returns: "0.1" (JavaScript string)
// Current code: JSON.parse("0.1") → 0.1 (WRONG - number instead of string)

This causes silent data corruption for any JSONB column storing numeric-looking strings.

Root Cause

override mapFromDriverValue(value: T["data"] | string): T["data"] {
  if (typeof value === "string") {
    try {
      return JSON.parse(value);  // ← Double-parses already-parsed values
    } catch {
      return value as T["data"];
    }
  }
  return value;
}

Fix

Only parse strings that look like raw JSON objects/arrays (starting with { or [), which indicates the driver returned unparsed JSON. String values from already-parsed JSON are returned as-is.

Related

Fixes #5485

[AlexBlokh]

this is something that will be properly fixed for all drivers and dialects and column types with the new reworked codecs system we gonna ship via codecs branch really soon, that've been a major problem which took time to design a proper solution for