refactor: consolidate getString/getFloat/getInt across read modules

[chmmou]

Context

Every read module under `internal/` (mailaccount, mailforward, mailfilter, mailinglist, account, server, domain, subdomain, dns, database, …) defines its own copy of `getString` / `getFloat` (and sometimes `getInt`) helpers around `soap.Value.Get`. They are byte-identical and grow with each new slice.

Proposal

Add a small internal helper package — e.g. `internal/soap/mapx` or expose `soap.Value` accessor methods like `MapString(key) string`, `MapFloat(key) float64`, `MapInt(key) int` — and migrate every read module to it in a single refactor PR.

Constraints / non-goals

• Refactor only; no behavioural change. Tests already pin the per-field shapes via fixtures, so they are the safety net.
• No new functionality; the consolidation should land as one `refactor:` PR after the in-flight read slices in Read modules: hosting (databases, FTP, samba, cronjobs, software, directory protection, ddns) #11 are done so the migration touches a stable surface.

Surfaced during the code-review of PR #55 (databases read slice).

[chmmou]

Status update (2026-05-09):

• The precondition stated when this issue was filed — "after the in-flight read slices in Read modules: hosting (databases, FTP, samba, cronjobs, software, directory protection, ddns) #11 are done" — is now met. Read modules: hosting (databases, FTP, samba, cronjobs, software, directory protection, ddns) #11 was closed on 2026-05-08 with all seven hosting read slices merged (feat: databases get/list via get_databases (with database_login filter) #55, feat: ftpusers get/list via get_ftpusers (with ftp_login filter) #57, feat: sambausers get/list via get_sambausers (with samba_login filter) #58, feat: cronjobs get/list via get_cronjobs (with cronjob_id filter) #59, feat: directoryprotection list via get_directoryprotection (with directory_path filter) #61, feat: softwareinstalls get/list via get_softwareinstall (with software_id filter) #62, feat: ddnsusers get/list via get_ddnsusers (with ddns_login filter) #63).

• Current scope of the consolidation (helpers found via grep -rn 'func getString\|func getFloat\|func getInt' internal/):

  • internal/account/decode.go — getString, getInt, getFloat
  • internal/cronjob/cronjob.go — getString, getInt
  • internal/database/database.go — getString, getFloat
  • internal/ddns/ddns.go — getString
  • internal/directoryprotection/directoryprotection.go — getString
  • internal/dns/dns.go — getString, getInt
  • internal/domain/domain.go — getString, getInt
  • internal/ftpuser/ftpuser.go — getString
  • internal/mailaccount/mailaccount.go — getString, getInt, getFloat
  • internal/mailfilter/mailfilter.go — getString
  • internal/mailforward/mailforward.go — getString
  • internal/mailinglist/mailinglist.go — getString
  • internal/sambauser/sambauser.go — getString
  • internal/server/server.go — getString
  • internal/softwareinstall/softwareinstall.go — getString
  • internal/subdomain/subdomain.go — getString, getInt
  • internal/usage/usage.go — getString, getInt, getInt64

  17 packages, ~28 helper copies. internal/usage/usage.go adds a getInt64 variant that the proposed common API should also cover.