Add Barstool::context() for storing custom context on recordings

[craigpotter]

Overview of change

Adds the ability to attach custom context to Barstool recordings, stored in a new nullable JSON context column:

use Saloon\Barstool\Barstool;

Barstool::context([
    'user_id' => auth()->id(),
    'tenant_id' => $tenant->id,
]);

// Or a single key:
Barstool::addContext('job', 'user-sync');

Every request recorded after this point stores the context on its row. getContext() and flushContext() are also available.

Implementation notes

• Context is stored as hidden data on Laravel's Context (Context::addHidden) under a namespaced key. This means it is carried into queued jobs automatically (set context in a controller, and API calls made inside a dispatched job still record it), it is reset between requests/workers by the framework, and it never leaks into the application's log context.
• The persist payload only includes the context key when context has actually been set. Existing installs can upgrade the package without running the new migration and nothing breaks — the column is only referenced once you opt in to the feature. This makes it a safe minor release.
• New add_context_to_barstools_table migration for existing installs (guarded with hasColumn, so it is a no-op on fresh installs where the create migration already includes the column).

Related

• Closes [Bug]: is it possible to store some context alongside the request data ( eg. current auth user, ... ) #7 — context (auth user, tenant, etc.) can now be stored alongside the request data.
• Complements the discussion on Add ability to supply X-Barstool-UUID in a request header #6 — the README now documents the UUID read-back pattern for correlating your own models with a Barstool recording, and there is a test locking that behaviour in.

Testing

• Six new Pest tests covering: context recorded on the row, merge/overwrite/flush semantics, null column and absent payload key when unset, context in queued payloads, and the UUID read-back correlation pattern.
• composer test (25 passed), composer analyse (PHPStan level 8, clean), composer format (clean).