Implement simplified Excel with SET/GET/SUM

Implement a simplified in-memory spreadsheet that supports three operations: `SET`, `GET`, and `SUM`, similar to basic Excel functionality. Assumptions and requirements: - The spreadsheet consists of cells identified by standard Excel-like coordinates: - Columns are single uppercase letters from `'A'` to `'Z'`. - Rows are integers from `1` to `1000`. - A cell ID is a string such as `'A1'`, `'B2'`, `'Z1000'`. - Each cell can either contain: - A numeric value (integer), or - A formula that is a sum of other cells or rectangular ranges of cells. You must support the following operations: 1. **SET(cellId, value)** - Set the given cell to a numeric integer value. - Any existing formula or previous value in that cell is overwritten. - Return the value set. 2. **GET(cellId)** - Return the current evaluated integer value of the cell. - If the cell contains a formula (from a `SUM` operation), its value is the sum of its referenced cells, recursively evaluated. 3. **SUM(cellId, refs)** - `cellId` is the target cell where we store a formula. - `refs` is a list of references. Each reference is either: - A single cell ID, e.g. `'B2'`, or - A rectangular range in the form `'A1:B2'`, which represents all cells whose column is between `A` and `B` inclusive and whose row is between `1` and `2` inclusive. - Store in `cellId` a formula that is defined as the sum of all cells in `refs` (expanding ranges into the constituent cells). - Return the evaluated sum of that formula. Behavioral example (your implementation should be consistent with this behavior): - `SET('A1', 1)` → returns `1` - `SET('B2', 2)` → returns `2` - `SUM('C1', ['A1:B2', 'B2'])` → returns `5` - `SUM('C1', ['B2'])` → returns `2` - `SET('C1', 5)` → returns `5` - `GET('C1')` → returns `5` - `SUM('D1', ['C1', 'A1'])` → returns `6` - `SET('A1', 10)` → returns `10` - `GET('C1')` → returns `14` (because `C1` still refers to `B2` whose value is `2`, so its formula sum is `2 + 10 + 2` in the example sequence) Additional requirements and edge cases: - Updating a cell via `SET` or `SUM` must correctly affect any other cells whose formulas depend (directly or transitively) on that cell, so that subsequent `GET` calls return up-to-date values. - There may be chains of dependencies, e.g. `A1` used by `B1`, which is used by `C1`, etc. - You must **handle potential cycles** in formulas. For example, if `A1` depends on `B1` and later `B1` is defined to depend on `A1`, there is a cycle. - Define and implement a reasonable behavior for cyclic dependencies (e.g., detect cycles during evaluation or update and prevent them, or return an error/special behavior). Clearly state your chosen behavior in code comments. - Aim for an efficient implementation that avoids recomputing large dependency graphs from scratch on every `GET`. Design and implement the data structures and methods to support these operations.