.Net: Bump package version to 1.82.0 (#14721)

### Motivation and Context

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Prepares the .NET packages for the 1.82.0 minor release, following the
version-only preparation used for 1.81.0.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

- Bump the shared `VersionPrefix` from `1.81.0` to `1.82.0`.
- Advance `PackageValidationBaselineVersion` from `1.80.1` to the latest
published version, `1.81.0`.
- No source, dependency, or public API changes in this PR.

Local validation used .NET SDK 10.0.403 on Windows and Debug
configuration. Commands below run from `dotnet`; output-directory
variables identify local session folders.

- `dotnet build src\SemanticKernel.Core\SemanticKernel.Core.csproj -c
Debug --tl:off --warnaserror`: passed for `net10.0`, `net8.0`, and
`netstandard2.0`, including Abstractions, with zero warnings and errors.
- `dotnet test
src\SemanticKernel.UnitTests\SemanticKernel.UnitTests.csproj -c Debug -f
net10.0 -p:TreatWarningsAsErrors=true --logger trx --results-directory
$TestResultsDirectory`: passed, 1,614 tests, zero failures or skips.
- `dotnet pack
src\SemanticKernel.Abstractions\SemanticKernel.Abstractions.csproj -c
Debug --no-build --no-restore --output $PackageOutputDirectory`: passed,
including compatibility validation against `1.81.0`.
- `dotnet pack src\SemanticKernel.Core\SemanticKernel.Core.csproj -c
Debug --no-build --no-restore --output $PackageOutputDirectory`: passed,
including compatibility validation against `1.81.0`.
- Verified the generated package versions and the Core-to-Abstractions
dependency are `1.82.0`.
- `dotnet format
src/SemanticKernel.Abstractions/SemanticKernel.Abstractions.csproj
--verify-no-changes --no-restore --verbosity diagnostic`: passed in the
CI image, `mcr.microsoft.com/dotnet/sdk:10.0`, through Ubuntu WSL.
- `dotnet format src/SemanticKernel.Core/SemanticKernel.Core.csproj
--verify-no-changes --no-restore --verbosity diagnostic`: passed in the
same CI container.
- `git diff --check`: passed.

The full repository build/test matrix and service-backed integration
tests were not run locally.

AI assistance: Copilot prepared the version bump, validation, and PR
description.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Author: rogerbarreto

dotnet/nuget/nuget-package.props

@@ -1,15 +1,15 @@
 <Project>
   <PropertyGroup>
     <!-- Central version prefix - applies to all nuget packages. -->
-    <VersionPrefix>1.81.0</VersionPrefix>
+    <VersionPrefix>1.82.0</VersionPrefix>
     <PackageVersion Condition="'$(VersionSuffix)' != ''">$(VersionPrefix)-$(VersionSuffix)</PackageVersion>
     <PackageVersion Condition="'$(VersionSuffix)' == ''">$(VersionPrefix)</PackageVersion>
 
     <Configurations>Debug;Release;Publish</Configurations>
     <IsPackable>true</IsPackable>
 
     <!-- Package validation. Baseline Version should be the latest version available on NuGet. -->
-    <PackageValidationBaselineVersion>1.80.1</PackageValidationBaselineVersion>
+    <PackageValidationBaselineVersion>1.81.0</PackageValidationBaselineVersion>
     <!-- Validate assembly attributes only for Publish builds -->
     <NoWarn Condition="'$(Configuration)' != 'Publish'">$(NoWarn);CP0003</NoWarn>
     <!-- Do not validate reference assemblies -->