Refactored service binding

[spoenemann]

I feel the service container approach introduced in #6 is too complicated. I propose to simplify it as done in this PR.

We define a service.Container utility where you can register (MustPut or MustOverride) and retrieve (Get or MustGet) service instances. There's no "injection" – every service simply keeps a pointer to the service container and retrieves things when they're needed.

Performance Impact

I added a helper program to run a standardized benchmark:

go run ./internal/bench -runs 30 -cpu 1

On main:

MB/s:        min 3.380, avg 3.465, max 3.520
ms/resource: min 1.4710, avg 1.4953, max 1.5310

On this PR:

MB/s:        min 3.400, avg 3.456, max 3.510
ms/resource: min 1.4740, avg 1.4991, max 1.5230

This is 0.25% slower than before, probably due to the hash map lookups.

[msujew]

Thanks, makes this a lot easier to understand.

[spoenemann]

With the service caching, we're even 0.3% faster than on main:

MB/s:        min 3.430, avg 3.477, max 3.580
ms/resource: min 1.4460, avg 1.4902, max 1.5110