partial for #18263

Caps the X11 forwarding sessions at a maximum port of 6200, and evicts the oldest session if we create new sessions while at the max.

Unit tests included higher in the stack.

Changes the TestServer_X11 test to use a memmapped file system, so we don't pollute the XAuthority file of the person running the test.

Moves `InProcNet` to `testutil` so that it can be reused by X11 forwarding tests (see up stack PRs).

relates to #18263


Refactors the x11Forwarder to accept a networking `interface` that we can fake out for testing. This isolates the unit tests from other processes listening in the port range used by X11 forwarding. This will become extremely important in up-stack PRs where we listen on every port in the range and need to control which ports have conflicts.

## Description

This PR improves the RBAC package by refactoring the policy, enhancing
documentation, and adding utility scripts.

## Changes

* Refactored `policy.rego` for clarity and readability
* Updated README with OPA section
* Added `benchmark_authz.sh` script for authz performance testing and
comparison
* Added `gen_input.go` to generate input for `opa eval` testing

…ore (#18630)

relates to #18263


Adds a unit test for X11 listener eviction when all ports in the allowed range are in use.

relates to #18263

Modifies the eviction unit test to include a port that is already claimed by an external process.

…18567)

fixes #18263

Adds support to bump `usedAt` for X11 forwarding sessions whenever an application connects over the TCP socket. This should help avoid evicting sessions that are actually in use.

Co-authored-by: EdwardAngert <17991901+EdwardAngert@users.noreply.github.com>

Fixes coder/internal#695

Retries initial connection to postgres in testing up to 3 seconds if we
see "reset by peer", which probably means that some other test proc just
started the container.

---------

Co-authored-by: Hugo Dutka <hugo@coder.com>

…18591)

![image](https://github.com/user-attachments/assets/4db64031-17a9-405c-a233-df2b758ddef5)

)

**Before:**
![Screenshot 2025-06-25 at 14 40
16](https://github.com/user-attachments/assets/cbc558f5-6eee-4133-afc9-2474f04a8a67)

**After:**
![Screenshot 2025-06-25 at 14 53
53](https://github.com/user-attachments/assets/3a638f60-d1e4-40a4-a066-8d69fe96c198)

Close #18617

Close #18184