fix: avoid scientific notation in CMR URL coordinate parameters

[stark256-spec]

Fixes #73.

Problem

Python switches to scientific notation for floats outside roughly [1e-4, 1e16) — for example str(0.00001) returns "1e-05". CMR rejects scientific notation in URL parameters with "is not a valid URL encoded point", so queries using very small coordinate values silently fail.

Fix

Adds _format_float(value) which uses str() as the base representation and only converts to a fixed-point decimal string when scientific notation is detected:

def _format_float(value):
    s = str(value)
    if "e" not in s and "E" not in s:
        return s                                        # already plain decimal
    return f"{float(value):.15f}".rstrip("0").rstrip(".")  # strip trailing zeros

_format_float is applied to all coordinate parameters: point, circle, polygon, bounding_box, and line.

Using str() as the base preserves the natural representation of each type — integers stay as "1000" (not "1000.0"), floats stay as "1.0" — so no existing behaviour changes for normal-range values.

Tests

All 122 existing tests pass. The fix is a one-commit change on top of develop.

[chuckwondo]

Thanks @stark256-spec. This is looking good. Please add some unit tests.