Fix shadow-cljs warnings that complain about marker protocol

[athos]

Although Pogonos now does not officially support shadow-cljs, while I was trying it privately, it told me there were some infer warnings, which clj -Rcljs -m cljs.main never ever complained:

------ WARNING #1 - :infer-warning ---------------------------------------------
 File: /path/to/pogonos/src/pogonos/nodes.cljc:19:1
--------------------------------------------------------------------------------
  16 |
  17 | (defrecord Partial [name indent])
  18 |
  19 | (defrecord Comment [body]
-------^------------------------------------------------------------------------
 Cannot infer target type in expression (. (. Comment -prototype) -pogonos$nodes$Invisible$)
--------------------------------------------------------------------------------
  20 |   Invisible)
  21 |
  22 | (defrecord SetDelimiter [open close]
  23 |   Invisible)
--------------------------------------------------------------------------------

------ WARNING #2 - :infer-warning ---------------------------------------------
 File: /path/to/pogonos/src/pogonos/nodes.cljc:22:1
--------------------------------------------------------------------------------
  19 | (defrecord Comment [body]
  20 |   Invisible)
  21 |
  22 | (defrecord SetDelimiter [open close]
-------^------------------------------------------------------------------------
 Cannot infer target type in expression (. (. SetDelimiter -prototype) -pogonos$nodes$Invisible$)
--------------------------------------------------------------------------------
  23 |   Invisible)
  24 |
--------------------------------------------------------------------------------

------ WARNING #3 - :infer-warning ---------------------------------------------
 File: /path/to/pogonos/src/pogonos/core.cljc:37:26
--------------------------------------------------------------------------------
  34 |   ([in opts]
  35 |    (let [buf (parse/make-node-buffer)
  36 |          out (fn [x]
  37 |                (when-not (satisfies? nodes/Invisible x)
--------------------------------^-----------------------------------------------
 Cannot infer target type in expression (. x -pogonos$nodes$Invisible$)
--------------------------------------------------------------------------------
  38 |                  (buf x)))
  39 |          opts (fixup-options opts #?(:clj partials/resource-partials))]
  40 |      (parse/parse in out opts)
  41 |      (with-meta
--------------------------------------------------------------------------------

Roughly, these warnings seem to complain about a marker protocol (i.e. Invisible). After some exploration, it turned out that removing the protocol from the two record implementations resolved the warnings.

This PR replaces the Invisible protocol with a new one named IVisibility, which has a single method. The change not only resolves the above issue, but also makes the caller code more straightforward. It is indeed a breaking change, but has almost no impact on user code, I guess.

[codecov]

Codecov Report

Merging #2 into master will decrease coverage by 0.08%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master       #2      +/-   ##
==========================================
- Coverage   90.25%   90.16%   -0.09%     
==========================================
  Files          10       10              
  Lines         718      722       +4     
  Branches       39       38       -1     
==========================================
+ Hits          648      651       +3     
- Misses         31       33       +2     
+ Partials       39       38       -1     

Impacted Files	Coverage Δ
src/pogonos/nodes.cljc	86.66% <60.00%> (-13.34%)	⬇️
src/pogonos/core.cljc	86.90% <100.00%> (+1.19%)	⬆️

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