Add changelog entry

Co-authored-by: Agustin Mista <agustin.mista@moduscreate.com>
Co-authored-by: Alexander Esgen <alexander.esgen@iohk.io>
Co-authored-by: Georgy Lukyanov <georgy.lukyanov@iohk.io>
Co-authored-by: Thomas BAGREL <thomas.bagrel@tweag.io>
Co-authored-by: Nicolas BACQUEY <nicolas.bacquey@tweag.io>
Co-authored-by: Nicolas "Niols" Jeannerod <nicolas.jeannerod@moduscreate.com>

Author: 6 people

ouroboros-consensus/changelog.d/20250918_104810_thomas.bagrel_object_diffusion.md

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+### Patch
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+- A bullet item for the Patch category.
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+- A bullet item for the Non-Breaking category.
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+
+### Breaking
+
+- Relies on a new version of `ouroboros-network` with support for ObjectDiffusion mini-protocol
+- Added support for `NodeToNodeV_16`
+- Added modules `Ouroboros.Consensus.MiniProtocol.ObjectDiffusion{.Inbound,.Outbound}` with implementations of the ObjectDiffusion protocol (quite similar/inspired from TX-submission, except that client = inbound, server = outbound)
+- Added module `Ouroboros.Consensus.MiniProtocol.ObjectDiffusion.ObjectPool.API` defining `ObjectPool{Reader,Writer}` interfaces, through which ObjectDiffusion accesses/stores the objects to send/that have been received.
+- Added modules `Ouroboros.Consensus.MiniProtocol.ObjectDiffusion.PerasCert` and `Ouroboros.Consensus.MiniProtocol.ObjectDiffusion.ObjectPool.PerasCert` containing definitions specific to `PerasCert` diffusion through the ObjectDiffusion mini-protocol 
+- Modifies `Ouroboros.Consensus.Node.Serialisation` to add CBOR serialisation (`SerialiseNodeToNode`) for `Point blk`, `Tip blk`, and  `PerasCert blk`
+- Modifies `Ouroboros.Consensus{.Node,.Node.Tracer,.Network.NodeToNode}` to wire-in PerasCertDiffusion similarly to other mini-protocols (e.g. TX-submission)
+- Added modules `Test.Consensus.MiniProtocol.ObjectDiffusion.Smoke` and `Test.Consensus.MiniProtocol.ObjectDiffusion.PerasCert.Smoke` with smoke tests for the general ObjectDiffusion mini-protocol and for the `PerasCert`-specific instance of it
+
+
+### Non-Breaking
+
+- Updates `Test.ThreadNet.Network` in `unstable-diffusion-testlib` accordingly to the changes made in `Ouroboros.Consensus.Network.NodeToNode`