Improve speed of quantity stringification (#2090)

* Skip unit conversion when stripping own units

* Update release history

Author: mattwthompson

docs/releasehistory.md

@@ -13,6 +13,7 @@ Releases follow the `major.minor.micro` scheme recommended by [PEP440](https://w
 ### Behavior changes
 
 ### Bugfixes
+
 - [PR #2052](https://github.com/openforcefield/openff-toolkit/pull/2052): Fixes bug where `Topology.from_pdb` couldn't load NH4+ ([Issue #2051](https://github.com/openforcefield/openff-toolkit/issues/2051))
 
 ### Miscellaneous
@@ -22,7 +23,9 @@ Releases follow the `major.minor.micro` scheme recommended by [PEP440](https://w
 - [PR #2078](https://github.com/openforcefield/openff-toolkit/pull/2078): Updates molecule cookbook molecule.from_qcschema()
 
 ### New features
+
 - [PR #2066](https://github.com/openforcefield/openff-toolkit/pull/2066): Improves runtime in some situations by making AmberToolsToolkitWrapper perform lazy evaluation of AmberTools version. (@vamironov)
+- [PR #2090](https://github.com/openforcefield/openff-toolkit/pull/2090): Improves runtime of force field serialization via faster `Quantity` stringification.
 
 
 ### Improved documentation and warnings

openff/toolkit/utils/utils.py

@@ -163,7 +163,7 @@ def quantity_to_string(input_quantity: Quantity) -> str:
         The serialized quantity
 
     """
-    unitless_value: float | int | NDArray | list = input_quantity.m_as(input_quantity.units)
+    unitless_value: float | int | NDArray | list = input_quantity.m
     # The string representation of a numpy array doesn't have commas and breaks the
     # parser, thus we convert any arrays to list here
     if isinstance(unitless_value, np.ndarray):