Bump kotlinx.collections.immutable to 0.5.0-beta01

[DmitryNekrasov]

Summary

• Bumps `kotlinx.collections.immutable` from 0.4.0 → 0.5.0-beta01 (one line in `gradle/libs.versions.toml`).
• No method renames: bitwarden-android uses the library as a read-only consumer, typing everything as `ImmutableList` / `ImmutableMap<K, V>` / `ImmutableSet`, so none of the renamed copy-returning methods on `Persistent*` types are visible at any call site. The compiler emits zero `kotlinx.collections.immutable` deprecation warnings after the bump.
• This PR is a test of the migration skill (`kotlin-tooling-immutable-collections-0-5-0-migration`) — head and base both on the fork. Not intended for upstream.

Test plan

• Full module compile: `:app` (Standard + Fdroid debug, main + UnitTest), `:authenticator` (debug + UnitTest), `:ui`, `:core` (main + UnitTest), `:testharness` — `BUILD SUCCESSFUL in 1m 47s`, zero `kotlinx.collections.immutable` deprecation warnings.
• Unit tests: `:core:testDebugUnitTest :ui:testDebugUnitTest` — `BUILD SUCCESSFUL` (includes `PersistentListExtensionsTest` covering the custom `persistentListOfNotNull` helper).
• No textual rewrites applied: 511 factory-function call sites (`persistentListOf`, `toImmutableList`, etc.) deliberately left unchanged — the skill is compiler-driven and the compiler had nothing to flag.

See `MIGRATION_REPORT.md` for per-phase details.

🤖 Generated with Claude Code

[DmitryNekrasov]

Superseded by upstream PR bitwarden#6919. Closing this fork-internal test PR.