Cache router, filter, and process handlers into funs

[NelsonVides]

Following the advise from https://www.erlang.org/doc/efficiency_guide/functions.html#function-calls

Caching callback functions into funs may be more efficient in the long run than apply calls for frequently-used callbacks.

Similar logic was applied in OTP itself in
erlang/otp#5831
erlang/otp#7419

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (3e8bcca) 83.89% compared to head (c7074ee) 83.90%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4068   +/-   ##
=======================================
  Coverage   83.89%   83.90%           
=======================================
  Files         526      526           
  Lines       33168    33172    +4     
=======================================
+ Hits        27826    27832    +6     
+ Misses       5342     5340    -2     

Files Changed	Coverage Δ
src/config/mongoose_config_spec.erl	100.00% <ø> (ø)
src/ejabberd_router.erl	78.40% <100.00%> (-0.18%)	⬇️
src/mongoose_packet_handler.erl	100.00% <100.00%> (ø)
src/mongoose_router.erl	87.50% <100.00%> (+1.78%)	⬆️
src/xmpp_router.erl	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

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[mongoose-im]

elasticsearch_and_cassandra_25 / elasticsearch_and_cassandra_mnesia / c7074ee
Reports root/ big
OK: 369 / Failed: 0 / User-skipped: 38 / Auto-skipped: 0

---

small_tests_24 / small_tests / c7074ee
Reports root / small

---

small_tests_25 / small_tests / c7074ee
Reports root / small

---

small_tests_25_arm64 / small_tests / c7074ee
Reports root / small

---

ldap_mnesia_24 / ldap_mnesia / c7074ee
Reports root/ big
OK: 2258 / Failed: 0 / User-skipped: 827 / Auto-skipped: 0

---

dynamic_domains_pgsql_mnesia_24 / pgsql_mnesia / c7074ee
Reports root/ big
OK: 4221 / Failed: 0 / User-skipped: 82 / Auto-skipped: 0

---

ldap_mnesia_25 / ldap_mnesia / c7074ee
Reports root/ big
OK: 2257 / Failed: 1 / User-skipped: 827 / Auto-skipped: 0

mod_global_distrib_SUITE:hosts_refresher:test_host_refreshing

{error,
  {{trees_for_connections_present,true,[{times,100,false}],ok},
   [{mongoose_helper,do_wait_until,2,
      [{file,"/home/circleci/project/big_tests/tests/mongoose_helper.erl"},
       {line,357}]},
    {mod_global_distrib_SUITE,test_host_refreshing,1,
      [{file,
         "/home/circleci/project/big_tests/tests/mod_global_distrib_SUITE.erl"},
       {line,384}]},
    {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1782}]},
    {test_server,run_test_case_eval1,6,
      [{file,"test_server.erl"},{line,1291}]},
    {test_server,run_test_case_eval,9,
      [{file,"test_server.erl"},{line,1223}]}]}}

Report log

---

dynamic_domains_mssql_mnesia_25 / odbc_mssql_mnesia / c7074ee
Reports root/ big
OK: 4218 / Failed: 0 / User-skipped: 85 / Auto-skipped: 0

---

dynamic_domains_pgsql_mnesia_25 / pgsql_mnesia / c7074ee
Reports root/ big
OK: 4221 / Failed: 0 / User-skipped: 82 / Auto-skipped: 0

---

dynamic_domains_mysql_redis_25 / mysql_redis / c7074ee
Reports root/ big
OK: 4195 / Failed: 0 / User-skipped: 108 / Auto-skipped: 0

---

pgsql_mnesia_24 / pgsql_mnesia / c7074ee
Reports root/ big
OK: 4604 / Failed: 0 / User-skipped: 89 / Auto-skipped: 0

---

internal_mnesia_25 / internal_mnesia / c7074ee
Reports root/ big
OK: 2404 / Failed: 0 / User-skipped: 681 / Auto-skipped: 0

---

pgsql_mnesia_25 / pgsql_mnesia / c7074ee
Reports root/ big
OK: 4604 / Failed: 0 / User-skipped: 89 / Auto-skipped: 0

---

mysql_redis_25 / mysql_redis / c7074ee
Reports root/ big
OK: 4590 / Failed: 0 / User-skipped: 103 / Auto-skipped: 0

---

mssql_mnesia_25 / odbc_mssql_mnesia / c7074ee
Reports root/ big
OK: 4601 / Failed: 0 / User-skipped: 92 / Auto-skipped: 0

---

ldap_mnesia_25 / ldap_mnesia / c7074ee
Reports root/ big
OK: 2257 / Failed: 1 / User-skipped: 827 / Auto-skipped: 0

mod_global_distrib_SUITE:hosts_refresher:test_host_refreshing

{error,
  {{trees_for_connections_present,true,[{times,100,false}],ok},
   [{mongoose_helper,do_wait_until,2,
      [{file,"/home/circleci/project/big_tests/tests/mongoose_helper.erl"},
       {line,357}]},
    {mod_global_distrib_SUITE,test_host_refreshing,1,
      [{file,
         "/home/circleci/project/big_tests/tests/mod_global_distrib_SUITE.erl"},
       {line,384}]},
    {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1782}]},
    {test_server,run_test_case_eval1,6,
      [{file,"test_server.erl"},{line,1291}]},
    {test_server,run_test_case_eval,9,
      [{file,"test_server.erl"},{line,1223}]}]}}

Report log

---

ldap_mnesia_25 / ldap_mnesia / c7074ee
Reports root/ big
OK: 2258 / Failed: 0 / User-skipped: 827 / Auto-skipped: 0

[arcusfelis]

yea, probably marginally faster.
but only because we store it in a persistent term.

If it was in ETS table than copying a bigger term would defeat the gains :D