REGEX frontend: white space and nesting bugfix

[reuterbal]

Discovered with IFS source files.

Two small fixes for the REGEX frontend patterns, with tests that triggered before the corresponding changes:

• Multiple or no white space around the end statement for procedures
• Matching of module procedures is now lazy to match internal subprograms in module procedures

[github-actions[bot]]

Documentation for this branch can be viewed at https://sites.ecmwf.int/docs/loki/274/index.html

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.83%. Comparing base (6b58fe7) to head (92c0c5c). Report is 32 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #274 +/- ## ======================================= Coverage 92.83% 92.83% ======================================= Files 102 102 Lines 18121 18121 ======================================= Hits 16823 16823 Misses 1298 1298 ``` | [Flag](https://app.codecov.io/gh/ecmwf-ifs/loki/pull/274/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ecmwf-ifs) | Coverage Δ | | |---|---|---| | [lint_rules](https://app.codecov.io/gh/ecmwf-ifs/loki/pull/274/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ecmwf-ifs) | `96.39% <ø> (ø)` | | | [loki](https://app.codecov.io/gh/ecmwf-ifs/loki/pull/274/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ecmwf-ifs) | `92.80% <ø> (ø)` | | | [transformations](https://app.codecov.io/gh/ecmwf-ifs/loki/pull/274/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ecmwf-ifs) | `92.20% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ecmwf-ifs#carryforward-flags-in-the-pull-request-comment) to find out more.

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