Input error handling

## Matrix Mode:
### Input O:
- [ ] Missing required columns (variable, coefficient)
- [ ] Make certain columns optional (lb, ub, type) — set default values:
1. lb = 0
2. ub = Inf
3. type = C
- [ ] Handle wrong letter case
- [ ] Handle missing column names (but the number of columns and their order is correct)
- [ ] Column type:
1. **coefficient, lb, ub:** numbers (strings that can be cast to numbers)
2. **type:** must be “C”, “B” or “I”
### Input A:

**Slam matrix:**
- [ ] Missing required columns (i, j, v)
- [ ] Handle wrong letter case
- [ ] Handle missing column names (but the number of columns and their order is correct)
- [ ] Column type: all must be numbers (strings that can be cast to numbers)

**Dense matrix:**
- [ ] Check if number of columns = number of rows in **Input O**
- [ ] Column type: all must be numbers (strings that can be cast to numbers)
### Input B

This is an **optional** input, there is an option to combine integrate Input B to Input A:
- [ ] Missing required columns (i, j, v)
- [ ] Handle wrong letter case
- [ ] Handle missing column names (but the number of columns and their order is correct)
- [ ] Column type:
1. **dir**: only allows “<=”, “>=”, “=” —we also need to handle change “==” to “=”, in case some users accidentally use “==”
2. **rhs:** only allows numbers (string that can be cast to numbers)