allow ramble to generate an empty env for injection

[rfbgo]

Previously the user has to specify an env explicitly, even if it was allowed to be empty.

    ==> Error: No defined environment matches required name gromacs

Ramble now creates a default empty env and allows packages to be injected into it as required. Detecting missing required packages still works the same

[gemini-code-assist]

Code Review

This pull request introduces auto-construction of undefined software environments when they are required, rather than raising an error immediately. It also adds a check to warn users if an auto-constructed environment contains no packages, along with corresponding unit tests. The feedback suggests replacing the deprecated logger.warn with logger.warning to adhere to modern Python logging standards.

[ramble-pr-bot]

Ramble Performance Test Metrics

Results produced with commit: 9bcc6ca

Test Name	Outcome	Duration (s)	Most Recent Run (s)	Last 5 Avg (s)
test_analyze_large_file	passed	2.1560	2.1005 (de4ccce)	2.0984
test_large_template_expansion	passed	1.7715	1.6327 (de4ccce)	1.6532
test_many_experiments	passed	26.5574	24.6595 (de4ccce)	25.4157
test_many_objects_defaults	passed	15.9377	14.4773 (de4ccce)	14.4945
test_matrix_filter_perf	passed	1.2489	1.1632 (de4ccce)	1.1704

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (de4ccce) to head (9bcc6ca).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1717   +/-   ##
========================================
  Coverage    93.48%   93.48%           
========================================
  Files          367      367           
  Lines        35916    35957   +41     
========================================
+ Hits         33575    33616   +41     
  Misses        2341     2341           

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