Derived Table support for @perspective-dev/viewer

[texodus]

This PR build on #3246 by adding support for deriving client.table(view) in the <perspective-viewer> UI, ViewerConfig and WorkspaceConfig.

Derived tables in perspective-viewer

• restoreWorkspace() / saveWorkspace() have a new a top-level derived_tables map. Each entry is the table its source View reads plus that view's config. Entries may chain through other derived tables and are built parent-first. The key follows the panels update rule: absent keeps, a value replaces, {} deletes all.
• Single-panel save() / restore(): the table field is now a TableRef, either a hosted table name or an inline derived-table definition recursing through its own table field. restore() reuses a structurally identical derived table or creates one under a generated name.
• "Subqueries" stack in the settings sidebar and Derive Table in the panel context menu, if supported by the client's
  view_derivations feature. The "New" menu lists derived tables with reader counts and a delete action.

row_number window aggregate

• New perspective-server window aggregate row_number: 1-based, dense position of the row in its partition's order_by order (already supported in DuckDB and Postgres Virtual Servers).
• Declared in GetFeatures for every source type, so the window editor offers it after any column. ClickHouse virtual servers (TS and Python) now declare it too.

Internal

• PSP_FAST=1: release build at -O1, no LTO, no wasm-opt. Cargo [profile.fast] and bundle --fast. pnpm run setup replaces the debug/fast confirms with one three-way "Build mode?" prompt so the two cannot coexist. I may try this with CI next.

Fixes

• Fixes Support "post-aggregation" expressions (or a multi-weight ratio-delta aggregate) for row-pivoted views #3198, expressions columns in derived tables are calculated on the aggregates (note the group_rollup_mode)
• Fixes Filtering on aggregated results (similar to SQL HAVING clause) #2685, similarly filter (or in this case another expression column with a boolean result for demo)
• Fixes How to only display the recent three rows in datagrid? #1751 via the row_number() window column aggregate.

Example

Expression column on aggregates

{
        "plugin": "Datagrid",
        "table": {
            "table": "superstore",
            "group_by": ["State"],
            "group_rollup_mode": "flat",
            "columns": ["Sales", "Profit"],
            "aggregates": {
                "Profit": ["weighted mean", ["Row ID"]],
                "Sales": ["weighted mean", ["Postal Code"]]
            }
        },
        "title": "Superstore",
        "group_by": ["State"],
        "expressions": {
            "\"Sales\" - \"Profit\"": "\"Sales\" - \"Profit\""
        },
        "columns": ["Sales", "Profit", "\"Sales\" - \"Profit\""]
    }

Top 3 most recent orders

{
        "plugin": "Datagrid",
        "table": "superstore",
        "sort": [["Order Date", "desc"]],
        "filter": [["New Column 1", "<=", 3]],
        "windows": {
            "New Column 1": {
                "column": "Row ID",
                "aggregate": "row_number",
                "order_by": ["Order Date", "desc"]
            }
        },
        "columns": ["Sales", "Customer Name", "Order Date"]
    }