refactor: share AuthenticationObj across muxed providers

[badarsebard]

Purpose of the PR

Share a single AuthenticationObj (and therefore a single cookie jar / session) across both muxed providers so cross-provider Terraform applies stop hitting 401s.

Linked JIRA issue(s)

• none

Summary of changes

This provider muxes provider_framework (terraform-plugin-framework) and provider_sdkv2 (terraform-plugin-sdk/v2) into a single binary. Before this change each provider built its own *AuthenticationObj in Configure, each with its own http.Client / cookie jar. A package-level refcount in providers/utils short-circuited the second provider's signin — but only to skip the API call, not to share the cookie. The result: whichever provider signed in second had the valid session; the other made API calls with an invalidated cookie and got 401s.

This PR replaces that machinery with a single shared session built lazily in Configure and torn down in main:

• providers/utils/session.go (new): InitSharedAuth(cacheKey, build) builds the *AuthenticationObj, performs GetPasswordSafeAuthentication, and caches both under a mutex. Both providers' Configure methods call it; since they compute the same cacheKey from the provider block they hit the cache and reuse one session. ShutdownSharedAuth() signs that session out. ResetSharedAuthForTest() is a test-only escape hatch.
  • cacheKey is derived from URL + apiVersion + credentials + verify_ca + cert name. Acceptance tests that rotate httptest URLs between cases naturally produce a different key and trigger a clean re-init — no per-test plumbing required.
• providers/utils/methods.go: removed Authenticate, SignOut, AuthMu, SignInCount, signAppinResponse, and DeleteAssetByID. File is now just TestResourceConfig + ValidateChangeFrequencyDays.
• providers/provider_framework/provider.go: Configure calls InitSharedAuth instead of building + signing in inline.
• providers/provider_sdkv2/provider.go + common.go: providerConfigure calls InitSharedAuth and returns a new *providerMeta{authObj, signAppin} instead of a raw *AuthenticationObj. The old authenticate(d, m) / signOut(d, m) wrappers in common.go are gone.
• main.go: calls utils.ShutdownSharedAuth() after tf5server.Serve returns (before any log.Fatal).
• All framework and sdkv2 resources / data sources / ephemerals: dropped the per-RPC utils.Authenticate(...) and utils.SignOut(...) calls. They now use the shared authenticationObj directly. SDKv2 sites changed m.(*auth.AuthenticationObj) → m.(*providerMeta) and read .authObj / .signAppin.
• providers/provider_framework/assets_resource.go: utils.DeleteAssetByID is gone; the 3 delete sites now call assets.NewAssetObj + DeleteAssetById inline.
• providers/provider_framework/managed_systems_by_database_resource.go: getManagedSystemObj no longer signs in; APISignOut removed entirely and its 3 call sites cleaned up.
• Tests: providers/utils/methods_test.go rewritten — old TestAuthenticate / TestSignOut / TestDeleteAssetByID removed, new TestInitSharedAuth_* and TestShutdownSharedAuth_* added. SDKv2 resource tests wrap their raw *AuthenticationObj in &providerMeta{authObj: …}. provider_test.go switched to a mock signin server since providerConfigure now performs the handshake.

Impacted areas: provider auth lifecycle (all resources/data sources across both providers). No user-facing schema changes; HCL is unchanged.

Checklist

Release

• Priority release required due to Hot fix / Escalation / Critical bug
• Priority release not required (can be released later with other stories or bugs fixes)

Testing

• dev — go build ./..., go vet ./..., and TF_ACC=1 go test ./... all green locally (utils, provider_framework, provider_sdkv2)
• automation (required for feature branch merges and significant changes)
• manual (required for feature branch merges and significant changes) — needs a manual terraform plan / apply against a real Password Safe instance that mixes framework and sdkv2 resources in one config to confirm 401s are gone

Automation

• no changes are required
• existing tests have been updated
• new tests have been added
• further changes are required by the automation team

[btfhernandez]

Replaced by: #196