perf(database): zero-allocation hex formatting for BLOB/Bytea and eliminate split in date cell rendering #1529

Problem

In postgres_result_cells.dart (lib/core/database/postgres_result_cells.dart):

1. postgresByteaHexDisplay loops over Uint8List and calls b.toRadixString(16).padLeft(2, '0') for each byte. For a 2KB binary blob, this creates 4,096 temporary strings.
2. In date-only cells, value.toIso8601String().split('T').first allocates a 2-element list and discards the second element on every date cell of every row (e.g. 50,000 lists for 50,000 rows).

Solution

• Use a static hex character lookup table (const _hexDigits = '0123456789abcdef') and write char codes directly without intermediate toRadixString or padLeft allocations.
• Extract the date substring (iso.substring(0, 10)) or format directly without split('T').

Benefits

• 0 intermediate string allocations per byte in binary cell rendering.
• 0 List allocations when displaying date columns in query results.