test: cover terminal and non-terminal + in updateClippingInformation

Add a positive regression case for a terminal + segment with a clipping
attribute, and a negative case asserting the non-terminal + precondition
fires. Also reflow the read-structure paragraph in DemuxFastqs so the
source no longer wraps mid-clause. Both per PR #1157 review feedback.

Author: tfenne

src/main/scala/com/fulcrumgenomics/fastq/DemuxFastqs.scala

@@ -245,11 +245,10 @@ object DemuxFastqs {
       |4. `S` identifies a set of bases that should be skipped or ignored
       |
       |At most one `<number><operator>` pair in a read structure may use a `+` sign in place of the number to denote
-      |"all remaining bases", and it may appear at any position in the read structure.  This is useful if, e.g.,
-      |fastqs have been trimmed and contain reads of varying length. Both reads must have template bases.  Any
-      |molecular identifiers will be concatenated using
-      |the `-` delimiter and placed in the given SAM record tag (`RX` by default).  Similarly, the sample barcode bases
-      |from the given read will be placed in the `BC` tag.
+      |"all remaining bases", and it may appear at any position in the read structure.  This is useful if, e.g., fastqs
+      |have been trimmed and contain reads of varying length. Both reads must have template bases.  Any molecular
+      |identifiers will be concatenated using the `-` delimiter and placed in the given SAM record tag (`RX` by default).
+      |Similarly, the sample barcode bases from the given read will be placed in the `BC` tag.
       |
       |Metadata about the samples should be given in either an Illumina Experiment Manager sample sheet or a metadata CSV
       |file.  Formats are described in detail below.

src/test/scala/com/fulcrumgenomics/umi/ExtractUmisFromBamTest.scala

@@ -447,5 +447,17 @@ class ExtractUmisFromBamTest extends UnitSpec with OptionValues {
     record("XT") = 40
     ExtractUmisFromBam.updateClippingInformation(record, Some("XT"), ReadStructure("20T10M70T"))
     record[Int]("XT") shouldBe 30
+
+    // terminal `+` is the only positive `+` case allowed; clip should shift by the same 10 as `10M90T`
+    record("XT") = 50
+    ExtractUmisFromBam.updateClippingInformation(record, Some("XT"), ReadStructure("10M+T"))
+    record[Int]("XT") shouldBe 40
+
+    // a non-terminal `+` cannot be combined with a clipping attribute, since translating the clip
+    // position would require knowing the read length
+    record("XT") = 30
+    an[Exception] should be thrownBy {
+      ExtractUmisFromBam.updateClippingInformation(record, Some("XT"), ReadStructure("10M+M5T"))
+    }
   }
 }