DOC: Update dev container and Copilot prompts to install mssql-py-core from NuGet

[Copilot]

mssql_py_core (the Rust/TDS native module required for bulkcopy) is distributed as a NuGet package and must be fetched separately via eng/scripts/install-mssql-py-core.sh. Previously, none of the dev environment docs or the devcontainer setup automated or documented this step.

Changes

.devcontainer/post-create.sh

• Runs eng/scripts/install-mssql-py-core.sh automatically after the C++ extension build
• Non-fatal: warns and prints retry instructions if it fails, rather than aborting setup
• Completion message conditionally shows ✅/⚠️ based on actual installation outcome

.github/prompts/build-ddbc.prompt.md

• Adds Step 2 dedicated to installing mssql_py_core from NuGet (macOS/Linux and Windows)
• Renumbers former Step 2 (Verify) → Step 3, former Step 3 (Clean Build) → Step 4
• Adds troubleshooting entries for No module named 'mssql_py_core' and wheel-not-found errors
• Updates one-liner to include the NuGet install step

.github/prompts/setup-dev-env.prompt.md

• Adds Step 3.5 for mssql_py_core NuGet install, with platform-specific commands
• Adds mssql_py_core import check to the final verification script
• Adds troubleshooting entry and updates the Quick Reference one-liner and packages table

.github/prompts/run-tests.prompt.md

• Adds test_019_bulkcopy.py to the test file reference table, flagged as requiring mssql_py_core
• Notes that bulkcopy tests auto-skip when mssql_py_core is absent
• Adds a dedicated troubleshooting entry for skipped bulkcopy tests

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update the copilot instructions/dev containers or any other readmes</issue_title>
<issue_description>Since the pre-requisites to running the bulkcopy capability in dev environment is to use mssql-py-core from Nuget,
we need to update the following

1. Dev container to automatically download the nuget and extract it.
2. Copilot instructions and build prompts to reflect the need to download the nuget and place the wheel appropriately.
3. Any other instructions in the repo which help with the dev guide.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update the copilot instructions/dev containers or any other readmes #450

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