Add Table and DataTable block support

[VictorHLi404]

Summary

• Implements `TableIF` and `DataTableIF` block interfaces following the existing `@Immutable` + `@HubSpotStyle` pattern used by every other block in the codebase
• Introduces a `blocks/table/` subfolder with a two-tier cell hierarchy: `TableCell` (`raw_text`, `rich_text`) and `DataTableCell extends TableCell` (adds `raw_number`), enforcing at compile time that `raw_number` cells are only valid in data tables
• Registers both `Table` and `DataTable` in `Block.java`'s `@JsonSubTypes` for polymorphic deserialization
• Extends `BlockElementLengthLimits` with shared table limits (`MAX_TABLE_ROWS`, `MAX_TABLE_COLUMNS`, `MAX_TABLE_BLOCK_ID_LENGTH`) and data-table-specific limits (`MIN_DATA_TABLE_ROWS`, `MAX_DATA_TABLE_PAGE_SIZE`)

New files

Production:

• `TableIF` — `table` block with `column_settings`, `@Check` enforcing row/column/block_id limits
• `DataTableIF` — `data_table` block with required `caption`, optional `page_size` and `row_header_column_index`, `@Check` enforcing min rows, consistent column counts, header-row-must-be-raw_text, and page_size bounds
• `table/TableCell` — polymorphic root for `raw_text` + `rich_text` cells
• `table/DataTableCell` — extends `TableCell`, adds `raw_number`
• `table/RawTextTableCellIF`, `table/RawNumberTableCellIF`, `table/RichTextTableCellIF`, `table/UnknownTableCell`, `table/TableColumnSettingIF`

Tests:

• `TableBlockTest` — 9 tests covering deserialization, round-trip serialization, and all `@Check` validation paths
• `DataTableBlockTest` — 14 tests covering the same plus data-table-specific constraints

Test plan

• `TableBlockTest` — all 9 tests pass
• `DataTableBlockTest` — all 14 tests pass
• Full `slack-base` module build passes

🤖 Generated with Claude Code

[yyakhnytsia]

Reviewed, left comments.

[yyakhnytsia]

Could you please check if we shouldn't include RawNumberTableCellIF here as well

[VictorHLi404]

In documentation it says that Tables supports RawNumberTableCell, but in practice / what's actually implemented it doesn't support it. Not sure where the right place to raise that issue is to Slack, but I've omitted RawNumberTableCell here because of that.

[yyakhnytsia]

LGTM.

[yyakhnytsia]

@VictorHLi404 Do you have access to merge this PR?