fix: analyzer diagnostics should point to parameters, not methods

[thomhurst]

Description

Throughout TUnit.Analyzers/, diagnostics consistently point to the method location instead of the specific parameter that has the issue:

Diagnostic.Create(Rules.MissingTimeoutCancellationTokenAttributes,
    context.Symbol.Locations.FirstOrDefault())  // Reports at method, not parameter

When the parameter is the problem, the diagnostic should point to it:

parameter.Locations.FirstOrDefault() ?? context.Symbol.Locations.FirstOrDefault()

CombinedDataSourceAnalyzer.cs line 93 already shows the correct pattern — apply it consistently.

Impact

Users are directed to the wrong location, making it harder to understand and fix the issue.