fix: resolve MariaDB JSON columns showing as binary hex data

[datlechin]

Summary

• MariaDB JSON columns were displayed as hex dumps (0x7B2261...) instead of readable JSON text in the data grid, cell editor, and Row Details sidebar
• Root cause: MariaDB stores JSON as LONGTEXT with utf8mb4_bin collation (charset 46). The driver only checked the BINARY flag to distinguish BLOB from TEXT, but MariaDB sets this flag on any column with a binary collation — including JSON. Fixed by also requiring charsetnr == 63 (true binary charset)
• Added mariadb_field_attr(MARIADB_FIELD_ATTR_FORMAT_NAME) as best-effort JSON type detection for proper json badge display
• JSON fields in Row Details sidebar now render in a scrollable monospaced text area instead of a single-line TextField

Test plan

• 24 unit tests added (MariaDBJsonDetectionTests) covering classifier, blob formatting, cell display, and type properties
• Connect to MariaDB with JSON columns → verify grid shows readable JSON
• Select row → Row Details sidebar shows JSON in scrollable textarea
• Refresh table multiple times → JSON display is consistent (no random toggling)
• Connect to MySQL → JSON columns still work via type 245
• Verify real BLOB columns still display as hex