[decimal] Implement the quantize() function (#44)

This pull request adds support for a new `quantize` function across
various files and updates dependencies. The most important changes
include the addition of the `quantize` function, updates to the
`mojoproject.toml` file, and the inclusion of new benchmarks and tests.

### Addition of `quantize` function:

* `src/decimojo/decimal.mojo`: Added the `quantize` method to the
`Decimal` struct to allow quantizing a `Decimal` to a specified
exponent.
* `src/decimojo/rounding.mojo`: Implemented the `quantize` function,
which rounds a value according to the exponent of the second operand.

### Updates to `mojoproject.toml`:

* `mojoproject.toml`: Added the `max` dependency and included
`test_quantize` and `bench_quantize` tasks.

### Inclusion of new benchmarks and tests:

* `benches/bench.mojo`: Added `bench_quantize` to the list of
benchmarks.
* `src/decimojo/__init__.mojo`: Updated imports to include the new
`quantize` function.

Author: forfudan

benches/bench.mojo

@@ -7,6 +7,7 @@ from bench_from_float import main as bench_from_float
 from bench_from_string import main as bench_from_string
 from bench_from_int import main as bench_from_int
 from bench_round import main as bench_round
+from bench_quantize import main as bench_quantize
 from bench_comparison import main as bench_comparison
 from bench_exp import main as bench_exp
 from bench_ln import main as bench_ln
@@ -25,6 +26,7 @@ fn main() raises:
     bench_from_string()
     bench_from_int()
     bench_round()
+    bench_quantize()
     bench_comparison()
     bench_exp()
     bench_ln()