Fix VerifyError on some environments

[athos]

When I load pogonos.reader in the Clojure CLI REPL on JVM 14, I run into a VerifyError like the following:

$ clj
Clojure 1.10.1
user=> (require 'pogonos.reader)
Syntax error (VerifyError) compiling new at (pogonos/reader.cljc:36:4).
Operand stack underflow
Exception Details:
  Location:
    pogonos/reader/FileReader.close()Ljava/lang/Object; @6: areturn
  Reason:
    Attempt to pop empty stack.
  Current Frame:
    bci: @6
    flags: { }
    locals: { 'pogonos/reader/FileReader' }
    stack: { }
  Bytecode:
    0x0000000: 2ab9 0090 0100 b0

user=>

The same goes for Clojure CLI on JVM 8 and lein repl on JVM 14, but NOT for lein repl on JVM 8.

I'm not really sure what is exactly causing this (maybe the difference of classloaders and/or some change in the bytecode verification logic matters?), but after digging into it for a while, I figured out this happens if the reader impls implement java.io.Closeable#close() (which overloads pogonos.protocols/IReader#close()).

My first design decision for making the readers implement java.io.Closeable was just for the user's convenience. Now, however, I don't think It's worthwhile to do so because:

• In most cases, we, as a user, don't need to handle the readers directly
• Even when we really do, we can use pogonos.protocols/IReader#close() instead of java.io.Closeable#close()

So, this PR removes the java.io.Closeable implementation from the readers to work around the VerifyError. This really is a breaking change, but its impact won't be so significant for the reasons above.

[codecov]

Codecov Report

Merging #1 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master       #1   +/-   ##
=======================================
  Coverage   90.25%   90.25%           
=======================================
  Files          10       10           
  Lines         718      718           
  Branches       39       39           
=======================================
  Hits          648      648           
  Misses         31       31           
  Partials       39       39           

Impacted Files	Coverage Δ
src/pogonos/core.cljc	85.71% <100.00%> (ø)

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