Fix the OmegaIm default: drop the int cast on LargeValue

[aoymt]

RFC: this changes a physics-facing default written into
modpara.def; please review the intended behavior before merging.

StdFace_main.c computed the spectrum default as

StdFace_PrintVal_d("OmegaIm", &StdI->OmegaIm, 0.01* (int)StdI->LargeValue);

The (int) cast truncates LargeValue: for LargeValue < 1 the
default collapses to exactly 0, and for any non-integer
LargeValue the presumably intended 0.01 * LargeValue is rounded
down to the previous 0.01 step (e.g. LargeValue = 6.75 gave
OmegaIm = 0.06 instead of 0.0675).

This PR drops the cast and updates the affected reference files.

Impact (measured over the reference suite)

Of the 65 modpara.def references containing OmegaIm:

category	count
used the truncated default with non-integer LargeValue → changes	34
integer LargeValue (truncation was a no-op)	24
OmegaIm set explicitly in the input	7

The 34 reference updates touch only the OmegaIm column of the
OmegaMax / OmegaMin lines (69 changed lines total); the base-mode
integration suite passes 94/94 with the fix.

Behavior change

HPhi spectrum / time-evolution runs that relied on the default will see
a slightly larger OmegaIm (or a non-zero one where it used to be 0
for weakly-coupled systems). Users who need the old value can set
OmegaIm explicitly. Suggest a release-note entry.

Notes for reviewers

• Verified to merge cleanly onto the current develop head (the
  momentum-mode additions to StdFace_main.c do not overlap this
  change); the base-mode suite passes 95/95 on the merged tree.
• The pytest (3.10) CI job may fail on this branch for an unrelated,
  pre-existing reason (tomllib is Python 3.11+ stdlib; fixed on the
  Python development line). This PR touches only src/ and test/*/ref/.

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