Add conditional interception via type predicate (#42)

[tillig]

Fixes #42.

Problem

There was no way to apply interception selectively. When using assembly scanning, EnableClassInterceptors/EnableInterfaceInterceptors applied interception to every scanned type, with no hook to intercept only some of them based on the type.

Solution

Add a shouldIntercept predicate (Func<Type, bool>) to both EnableClassInterceptors and EnableInterfaceInterceptors, evaluated against the implementation type. This matches the shape suggested on the issue:

builder.RegisterAssemblyTypes(asm)
       .AsClosedTypesOf(typeof(ICommandHandler<,>))
       .EnableInterfaceInterceptors(t => t.IsDefined(typeof(AuditAttribute)))
       .InterceptedBy(typeof(LoggingInterceptor));

All new overloads are additive — every existing signature is unchanged, preserving binary compatibility (this is a strong-named assembly).

Method	New overloads
EnableInterfaceInterceptors	(Func<Type,bool>) and (ProxyGenerationOptions?, Func<Type,bool>?)
EnableClassInterceptors (concrete & scanning)	(Func<Type,bool>) and (ProxyGenerationOptions, Func<Type,bool>?, params Type[])

Semantics

The predicate is evaluated at different times for the two styles, because they work differently:

• Interface interception is resolve-time middleware, so the predicate is evaluated against the resolved implementation type (ctx.Instance.GetType()). When it returns false the instance is returned without a proxy (and the interface-only guard is skipped, since no proxy is attempted).
• Class interception rewrites the implementation type to a proxy subclass at registration time, so the predicate is evaluated per type at registration. When it returns false the registration is left untouched (real type, no proxy). Per-instance conditionality is not possible for class interception by construction.

Both behaviors are covered by XML docs and code comments.

Tests

New fixture ConditionalInterceptionFixture (7 tests):

• Applies / skips the proxy for both interface and class interception based on the predicate.
• Predicate applies per-type under assembly scanning for both styles.
• Null-registration guard for the new overloads.

Full suite green on net8.0 and net10.0; clean Release build (warnings-as-errors + analyzers) and dotnet format clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.71%. Comparing base (e63ef5c) to head (a6fd591).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #64      +/-   ##
===========================================
+ Coverage    89.34%   90.71%   +1.37%     
===========================================
  Files            2        2              
  Lines          122      140      +18     
  Branches        21       23       +2     
===========================================
+ Hits           109      127      +18     
  Misses           6        6              
  Partials         7        7              

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