i.in.spotvgt: bug fixes

[jayneel-shah18]

This PR addresses the four issues in the i.in.spotvgt module that previously led to incorrect imports or completely null raster outputs as highlighted in #6175.

Summary of Changes:

• Line if f < 2: caused type error due to comparison of list directly, it has been correctly fixed as if len(f) < 2:
• Previously, qname = spotname.replace("NDV", "SM") resulted in missing file error due to missing extension. This has been fixed by changing it to qname = spotname.replace("NDV", "SM") + ".HDF"
• In the old version,

rules = [
    r + "\n"
    for r in [
        "8 50 50 50",
        ...
    ]
]
gs.write_command("r.colors", map=smfile, rules="-", stdin=rules)

raised TypeError as stdin can only accept string or bytes. This has been fixed by modifying it to:

rules = """8 50 50 50
11 70 70 70
...
252 green
"""

• Line gs.use_temp_region() caused the output map to be null, since the temporary region prevented g.rename and r.mapcalc results from being preserved in main mapset. This line has been commented out.

This PR closes #6175.