docs: refresh package READMEs and split Interface README

[vbreuss]

• Rewrite the four Docs/Nuget/*.md package READMEs to reflect current functionality (PeriodicTimer, replay notifications, statistics, OS simulation, async zip overloads, full ACL surface) and link to docs.testably.org/Abstractions/.
• Add Docs/Nuget/FileSystemInterface.md and repoint the Testably.Abstractions.FileSystem.Interface csproj at it, so that package no longer ships the shared Interface.md that described ITimeSystem and IRandomSystem it does not contain.
• Drop the stale Expect.That example from Testing.md; the bullets describe the surface and the docs site has full examples.
• Update root README.md docs links to the /Abstractions/ slug and expand "BCL" on first use as "base class library (BCL)".
• Update slug casing in index.mdx

[Copilot]

Pull request overview

This PR refreshes NuGet package READMEs to better reflect current Testably.Abstractions features and splits the file-system-interface package README so it no longer ships a shared interface README describing unrelated APIs.

Changes:

• Updated root README.md to point documentation links at the new docs slug and expanded “base class library (BCL)” on first use.
• Rewrote package READMEs under Docs/Nuget/ (Testing, Interface, Compression, AccessControl) and added a new FileSystemInterface.md.
• Repointed Testably.Abstractions.FileSystem.Interface to ship and reference the new package-specific README.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
Source/Testably.Abstractions.FileSystem.Interface/Testably.Abstractions.FileSystem.Interface.csproj	Points package README to the new file-system-interface-specific markdown.
README.md	Updates top-level documentation links and wording in the project overview.
Docs/Nuget/Testing.md	Replaces long example with a condensed feature/links-focused package README.
Docs/Nuget/Interface.md	Updates interface package README to current scope and doc links.
Docs/Nuget/FileSystemInterface.md	Adds a dedicated README for the file-system interface-only package.
Docs/Nuget/Compression.md	Updates compression package README and docs link.
Docs/Nuget/AccessControl.md	Updates access-control package README and docs link.

Comments suppressed due to low confidence (2)

README.md:47

• Docs URLs appear to be lower-case (/abstractions/… per Docs/pages/docs/index.mdx). This link uses /Abstractions/getting-started; consider using https://docs.testably.org/abstractions/getting-started to avoid case-sensitive 404s.

Then register the implementations in your DI container - see [Getting Started](https://docs.testably.org/Abstractions/getting-started).

README.md:60

• Docs URLs appear to be lower-case (/abstractions/… per Docs/pages/docs/index.mdx). This migration-guide link uses /Abstractions/...; consider switching to https://docs.testably.org/abstractions/migration-from-testableio.

## Already on TestableIO?

`Testably.Abstractions` shares the `IFileSystem` interface with [TestableIO.System.IO.Abstractions](https://github.com/TestableIO/System.IO.Abstractions), so production code stays untouched. See the [migration guide](https://docs.testably.org/Abstractions/migration-from-testableio).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud