Fix intermittent parallel build failure in lib/libnfu

[underwoo]

Under make -j, make scheduled two independent jobs that both compiled
libnfu/nfu.F90: the .F90.o rule (producing nfu.o for libnfu.a) and the
.F90.$(FC_MODEXT) suffix rule (producing nfu_mod.mod for
nfu_compress.o's prerequisite). Because AM_FCFLAGS uses $(FC_MODOUT)$(@d),
both gfortran processes wrote to the same libnfu/nfu_mod.mod0 temp file
and raced to rename it, causing the intermittent error:

f951: Fatal Error: Cannot rename module file 'libnfu/nfu_mod.mod0'
to 'libnfu/nfu_mod.mod': No such file or directory

Fix by adding an explicit no-op rule in lib/libnfu/local.mk:

libnfu/nfu_mod.$(FC_MODEXT): libnfu/nfu.$(OBJEXT)
    @:

This overrides the .F90.$(FC_MODEXT) suffix rule so nfu.F90 is compiled
only once. nfu_mod.mod is treated as a side effect of building nfu.o,
and nfu_compress.o waits for it via the existing prerequisite.

Also replace the duplicate clean-local rule in local.mk (which produced
a make warning) with CLEANFILES += entries, and add CLEANFILES = in
lib/Makefile.am to initialise the variable before local.mk uses +=.

Fix a typo in tools/simple_hydrog/lakes/Makefile.am: the prerequisite
horiz_intrep.$(OBJEXT) did not match any source file; corrected to
horiz_interp.$(OBJEXT).

Closes: #405

Description
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Fixes # (issue)

How Has This Been Tested?
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Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[ilaflott]

i always find the CI here slippery because the branch/fork label doesn't get associated to the next jobs triggered, so making sure i'm viewing the right distcheck since you have two PRs right now:

the latest commit triggered FRE-NCTools CI --> ✅

that triggers FRE-NCTools Check Expensive --> ✅

that triggered... this good run of distcheck... or this bad run of distcheck?