[BUG] Python API background value different from what's expected

### Environment

**Operating System:** Linux
**Version / Commit SHA:** master

### Describe the bug

Something it's wrong with the python wrappers for `FloatGrid`. I'm trying to debug this issue myself but so far I haven't reach anywhere. Looks like the precision of floating point numbers is messing around, or sometihng similar.

I manage to narrow down the error to a minimalistic example.

**NOTE** This problem only appears in the Python wrappers in `pyopenvdb.so`, not a C++ API issue.

### To Reproduce

#### C++ Example

**Code:**

```cpp
#include

#include

using std::cout;
using std::endl;

int main() {
openvdb::initialize();
const float background_value = 0.3;
openvdb::FloatGrid::Ptr grid = openvdb::FloatGrid::create(background_value);

grid->print();
cout << "grid->background() = " << grid->background() << endl;
cout << std::boolalpha << (grid->background() == background_value) << endl;
return 0;
}
```

**Output:**

```sh
Information about Tree:
Type: Tree_float_5_4_3
Configuration:
Root(0), Internal(32^3), Internal(16^3), Leaf(8^3)
Background value: 0.3
Transform:
voxel size: 1
index to world:
[1, 0, 0, 0]
[0, 1, 0, 0]
[0, 0, 1, 0]
[0, 0, 0, 1]

grid->background() = 0.3
true
```

#### Python Example

**Code:**

```python
import pyopenvdb as vdb

background_value = float(0.3)
grid = vdb.FloatGrid(background_value)
print(grid.info())
print("grid.background =", grid.background)
print(grid.background == background_value)
```

**Output:**

```sh
Information about Tree:
Type: Tree_float_5_4_3
Configuration:
Root(0), Internal(32^3), Internal(16^3), Leaf(8^3)
Background value: 0.3
Transform:
voxel size: 1
index to world:
[1, 0, 0, 0]
[0, 1, 0, 0]
[0, 0, 1, 0]
[0, 0, 0, 1]

grid.background = 0.30000001192092896
False
```

### Expected behavior

As shown in the example, the value `0.3` gets interpreted as `0.30000001192092896` when using the Python API. Which seems strange...

Moreover, the comparission `grid.background == background_value` return `False`, **only** on the Python example, which confirms that something is "wrong".

### Additional context

Any ideas on where to look for this?
The problem with this error is that when working with python vdb grids, the background value doesn't get propperly interpreted, leading to a denser vdb representation(since `0.3` is not a background value anymore, it will be considered an active value on the grid)

Start with the pyopenvdb.so FloatGrid constructor and background property, comparing their behavior with the C++ FloatGrid example in the issue. Confirm the conversion of 0.3 and the equality result, then verify that Python-created grids retain the intended background value without causing equivalent values to become active.

Written by the indexing model from the issue text.