std.format spec conflict: docs say "follows Python rules" but std.jsonnet rejects booleans for numeric format codes

## Summary

There is a conflict between the official documentation and the reference implementation (`std.jsonnet`) regarding how `std.format` handles boolean values with numeric format codes.

## Documentation says

From https://jsonnet.org/ref/stdlib.html#std-format:

> The string formatting follows the same rules as Python.

In Python, `bool` is a subclass of `int`, so all numeric format codes accept booleans:

```python
>>> "%d" % True
'1'
>>> "%f" % True
'1.000000'
>>> "%x" % True
'1'
>>> "%s" % True
'True'
```

## Reference implementation says

In `std.jsonnet`, the `format_code` helper explicitly checks:

```jsonnet
if std.type(val) != 'number' then
error 'Format required number at ' + i + ', got ' + std.type(val)
```

Since `std.type(true)` returns `'boolean'` (not `'number'`), all numeric format codes reject booleans:

```
std.format("%d", true) → ERROR: "Format required number at 0, got boolean"
std.format("%f", true) → ERROR
std.format("%x", true) → ERROR
```

Only `%s` works: `std.format("%s", true) → "true"`

## The conflict

| Expression | Python behavior (per docs) | std.jsonnet behavior (per impl) |
|---|---|---|
| `"%d" % true` | `"1"` | ERROR |
| `"%f" % true` | `"1.000000"` | ERROR |
| `"%x" % true` | `"1"` | ERROR |
| `"%s" % true` | `"True"` | `"true"` |

This causes confusion for implementors: should a compliant Jsonnet implementation follow the documented Python behavior (accept booleans) or the std.jsonnet implementation (reject booleans)?

## Question

Which is the intended behavior?

- **(A)** The documentation is correct — `std.format` should follow Python's rules and accept booleans for numeric codes (meaning `std.jsonnet` has a bug)
- **(B)** The implementation is correct — `std.format` should reject booleans for numeric codes (meaning the documentation should be updated to remove the "follows Python" statement)

## Context

This was discovered in sjsonnet where we initially implemented option (A) (following Python), then reverted to match `std.jsonnet`'s behavior. See: https://github.com/databricks/sjsonnet/pull/1016

Start with the std.format documentation at the linked stdlib reference and the format_code helper in std.jsonnet, then compare the behavior described there with the examples in the issue. Review the linked sjsonnet PR for implementation context; done means the intended boolean behavior is decided and the documentation and reference implementation no longer conflict.

Written by the indexing model from the issue text.