Decode catalog numbers strictly and add the changelog fragment

Route tleCatalogNumber() and noradIdFromSatnum() through one decoder that
accepts only plain digits or a valid Alpha-5 field. parseInt and Number()
read '2554A', '255 4', '-1234', '0x1F0', '1.5' and blank as numbers; they
now return null/NaN. Digit satnums of any length still decode, so OMM
satrecs numbered past 99999 keep working.

Add a layer test that several Alpha-5 satellites survive ingestion dedupe,
the changelog fragment for #767, and note in CURRENT-STATE that this is
Alpha-5 TLE compatibility and malformed fields are rejected.

changelog.d/767-alpha5-catalog-numbers.md

@@ -0,0 +1,11 @@
+- Read satellite catalog numbers written in Alpha-5, the TLE spelling of
+  numbers above 99999: a letter for the first two digits, skipping I and O
+  (`A0000` is 100000, `Z9999` is 339999). The satellites layer converted such a
+  field to `NaN`, so every Alpha-5 satellite shared one catalog entry and all
+  but the first were dropped as duplicates; the satellite tools read the same
+  field as no number, so such a satellite could not be found by it. The layer
+  and the tools now decode the field in `src/sources/tle.js`, and reject a
+  malformed one (a sign, decimal point, hex, embedded space or stray letter)
+  instead of reading part of it as a number. This is Alpha-5 TLE
+  compatibility: CelesTrak's TLE feed carries no satellite above 99999, which
+  needs the OMM feed (#1191) (Honorius Neogy, #767, fixes #751).