refactor: Remove redundant WithImage() calls in Testcontainers setup

[Copilot]

Addresses code review feedback from PR #102 identifying redundant image specifications in Testcontainers builder setup.

Changes

• PostgreSqlBuilder: Use postgres:16-alpine directly in constructor instead of overriding postgres:16
• OracleBuilder: Use gvenzl/oracle-xe:21.3.0-slim-faststart directly instead of overriding 21-slim-faststart
• MySqlBuilder: Remove duplicate .WithImage("mysql:8.0") call
• Remove outdated.txt (CI-generated dotnet outdated output) and add to .gitignore

Before

var container = new PostgreSqlBuilder("postgres:16")
    .WithImage("postgres:16-alpine")
    .Build();

After

var container = new PostgreSqlBuilder("postgres:16-alpine")
    .Build();

Each container builder now has a single, explicit image specification in the constructor.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.example.com
  • Triggering command: /opt/oracle/product/21c/dbhomeXE/bin/oracle oracleXE (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) 386bfa5b8ba7f0d2175a1bc6b5d3081abed3effbd675b67863a27658c5180b40 9 (dns block)
  • Triggering command: /opt/oracle/product/21c/dbhomeXE/bin/oracle oracleXE (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) (dns block)
  • Triggering command: /opt/oracle/product/21c/dbhomeXE/bin/oracle oracleXE (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) 30249636079ce444548eb83bd11c73ac--root e658d91cc546132f55eac8e77042cf4c/var/run/docker/runtime-runc/moby conf�� ntime.v2.task/moby/1a3437dd6993a/run/containerd/io.containerd.runtime.v2.task/moby/955514d6e25e7xe_w000_XE --local 62d13fb956eca5b8ab9a7ae02369b147ba0/log.json 2e4d6cbe8c8a119c/usr/sbin/iptables 0d2175a1bc6b5d30--wait (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)