…Version

ServiceVersion previously rewrote +env+ and +version+ inputs:
  @env     = env.to_s.empty? ? 'none' : env.to_s
  @Version = version.to_s.empty? ? 'none' : version.to_s

Drops the rewriting — both fields now pass through unchanged. Empty
strings stay empty strings; nil stays nil. ServiceVersion's role is
to wrap a payload, not to sanitize inputs; defaulting belongs at the
caller (Component) where the source of env/version is known and the
sentinel choice (if any) can be made deliberately.

Master has no non-test callers of +ServiceVersion.new+ (verified via
+grep -rn 'ServiceVersion.new' lib/+ — no matches), so this is
contained to the spec changes in this PR.

The four +converts ... to "none"+ tests are replaced with four
+passes ... through unchanged+ tests covering the same nil/empty
inputs, asserting on the new pass-through behavior. The two +to_h+
tests for +none+ defaulting are similarly replaced.

Extracted from #5431 to land the behavior change independently of
the broader symbol-database upload work.

Note on pre-existing failure: +to_json produces valid JSON for
complete Ruby payload+ (line 142) was already failing on master with
+NameError: uninitialized constant Datadog::SymbolDatabase::Symbol+ —
the spec file is missing +require 'datadog/symbol_database/symbol'+.
Out of scope for this PR; not addressed here.

Verification:
- bundle exec rspec spec/datadog/symbol_database/service_version_spec.rb
  → 14 pass, 1 fail (the pre-existing failure described above)
- bundle exec steep check lib/datadog/symbol_database/service_version.rb
  → No type error detected.
- bundle exec rake standard → clean

Co-Authored-By: Claude <[email protected]>

The test +to_json produces valid JSON for complete Ruby payload+
constructs +Datadog::SymbolDatabase::Symbol.new(...)+ but the spec
file was missing +require 'datadog/symbol_database/symbol'+. The test
was failing on master with:

  NameError: uninitialized constant Datadog::SymbolDatabase::Symbol

Add the missing require. The spec is already in this PR's diff for
the +none+ defaulting changes, so addressing the failure here keeps
this branch's CI green. Flagged as out-of-scope in the original PR
body — that was hand-waving; the fix is trivial and the file is
already being modified.

Verification:
- bundle exec rspec spec/datadog/symbol_database/service_version_spec.rb
  → 15 examples, 0 failures (up from 14/15)

Co-Authored-By: Claude <[email protected]>