feat: Initialize Strata.Excel.Core library with export, import, and test utilities

This commit introduces the `Strata.Excel.Core` project, a .NET library built on ClosedXML for robust Excel document generation and data import.

Key features include:
- **Export:** Flexible data export to Excel, supporting custom formatting, titles, subtitles, humanized headings, and batched processing for large datasets. Includes `ExcelContentResult` and `ZipFileContentResult` for ASP.NET Core integration.
- **Import:** Utilities to easily import data from Excel worksheets into C# objects.
- **Test Utilities:** Comprehensive helpers for comparing Excel workbooks in tests, handling resource extraction, and performing load tests.
- **Build Infrastructure:** Sets up a Dockerfile for building the library, including SonarQube and Dependency-Check scanning.
- **Project Structure:** Establishes `.gitignore`, `.dockerignore`, `nuget.config`, and a `README.md` with usage instructions and versioning guidelines.

This foundational commit provides a reusable and well-tested framework for Excel operations within Strata applications.

Dockerfile.lib

@@ -0,0 +1,89 @@
+ARG PROJECT=Strata.Excel.Core
+ARG VERSION=0.0.0
+ARG SONARURL=''
+ARG SONARLOGIN=''
+ARG SONARBRANCH=''
+
+###############
+# Build image #
+###############
+FROM ecr.ops.stratanetwork.net/strata.microsoft.dotnet.sdk:6.0 AS build
+ARG PROJECT
+ARG VERSION
+ARG SONARLOGIN
+ARG SONARURL
+ARG SONARBRANCH
+
+RUN apt-get --allow-releaseinfo-change update && apt-get install -y libgdiplus
+
+WORKDIR /src
+
+# Copy project files and restore
+COPY ["${PROJECT}.sln", "${PROJECT}.sln"]
+COPY src/**/*.csproj ./
+RUN for file in $(ls *.csproj); do mkdir -p src/${file%.*}/ && mv $file src/${file%.*}/; done
+COPY tests/**/*.csproj ./
+RUN for file in $(ls *.csproj); do mkdir -p tests/${file%.*}/ && mv $file tests/${file%.*}/; done
+
+RUN dotnet restore "${PROJECT}.sln" \
+    --source https://api.nuget.org/v3/index.json \
+    --source https://proget.sdt.local/nuget/nuget/v3/index.json
+
+
+# Copy files and build
+COPY . .
+
+RUN if [ "${SONARLOGIN}" != "" ] ; then dotnet sonarscanner begin \
+   /k:"${PROJECT}" \
+   /d:sonar.scm.provider=git \
+   /d:sonar.host.url="${SONARURL}" \
+   /d:sonar.login="${SONARLOGIN}" \
+   ${SONARBRANCH} \
+   /d:sonar.cs.opencover.reportsPaths="/src/cover.xml" \
+   /d:sonar.dependencyCheck.jsonReportPath=/src/buildlogs/dependency-check-report.json \
+   /d:sonar.dependencyCheck.htmlReportPath=/src/buildlogs/dependency-check-report.html \
+   /v:sonar.projectVersion="${VERSION}"; fi
+
+
+RUN dotnet build "${PROJECT}.sln" \
+    --configuration Release \
+    --no-restore
+
+# Run unit tests
+RUN dotnet test "${PROJECT}.sln" \
+    --configuration Release \
+    --no-restore \
+    --no-build \
+    --verbosity=normal \
+    -p:CollectCoverage=true \
+    -p:CoverletOutputFormat="opencover" \
+    -p:CoverletOutput=/src/cover.xml
+
+RUN dotnet pack "src/Strata.Excel.Core/Strata.Excel.Core.csproj" \
+    --configuration Release \
+    --no-restore \
+    --no-build \
+    --include-symbols \
+    --include-source \
+    --output /pack \
+    -property:PackageVersion=${VERSION}
+
+RUN dotnet pack "src/Strata.Excel.TestUtilities/Strata.Excel.TestUtilities.csproj" \
+    --configuration Release \
+    --no-restore \
+    --no-build \
+    --include-symbols \
+    --include-source \
+    --output /pack \
+    -property:PackageVersion=${VERSION}
+
+
+RUN if [ "${SONARLOGIN}" != "" ] ; then \
+    /dc/dependency-check/bin/dependency-check.sh -f JSON -f HTML -s . -o ./buildlogs \
+    --suppression ./sonarsuppressions.xml \
+    --noupdate --nodeAuditSkipDevDependencies --disableNodeJS \
+    --dbDriverName "com.microsoft.sqlserver.jdbc.SQLServerDriver" \
+    --connectionString "jdbc:sqlserver://ddensqldevops01.sdt.local;Database=DependencyCheck;encrypt=true;trustServerCertificate=true;" \
+    --dbUser "dcuser" --dbPassword "${SONARLOGIN}" && \
+    dotnet sonarscanner end /d:sonar.login="${SONARLOGIN}"; \
+    fi