Add typed assertion helpers and tests for errors, filesystem, floats, slices, maps, readers, and URLs

[nfisher]

Motivation

• Expand the set of typed assertion helpers to make table-driven and generic tests more expressive and convenient across common types and behaviors.
• Provide assertions for I/O and URL validation to reduce boilerplate in tests that need to inspect readers and parsed URLs.

Description

• Added typed assertion implementations in error.go, filesystem.go, float.go, slice.go, reader.go, and url.go, including helpers such as NilError, ErrorContains, FileExists, NoFileExists, Float(...).CloseTo, Slice(...).Contains, Reader(...).EqualToString, and URL(...)/ParseURL(...) with query helpers.
• Extended map assertions in map.go with HasKey, NotHasKey, KeysExactly, NotEmpty/IsNotEmpty, NotContains, Len, WithItem, WithItems, and WithoutItems to support more map-centric checks.
• Added convenience aliases and tweaks such as Number(...).NotEqual, Str(...).NotContains, and Str(...).NotEmpty in number.go and string.go.
• Added comprehensive unit tests for each assertion in new _typed_test.go files and a small test helper file typed_assertion_helpers_test.go providing makeTempDirAndFile, testURL, and testMap utilities.

Testing

• Ran the test suite with go test ./... which exercised the new typed assertion tests in the added files such as error_typed_test.go, filesystem_typed_test.go, float_typed_test.go, slice_typed_test.go, map_typed_test.go, reader_typed_test.go, and url_typed_test.go.
• All newly added unit tests passed successfully under the executed test run.

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Codex Task